Clang assertion failed: Access != AS_none && "Access specifier is AS_none inside a record decl" when using address-of-label in nested struct array bound

### Link for quick verification: https://godbolt.org/z/PMvv5eWhT
```c
int main() {
int a;
struct {
int j[a ? (&&m) : (&&m)];
} s;
}
```
Go back to `clang 2.9.0 (asertions)`.
The following code triggers an ICE in Clang. It appears that when Clang's Sema attempts to resolve a label address (`&&label`) within the array bound of a nested struct member, the access specifier check fails because the context is incorrectly identified or not properly initialized for this specific GCC extension.

## Stack dump:
```console
clang++: /root/llvm-project/llvm/tools/clang/lib/AST/DeclBase.cpp:1138: bool clang::Decl::AccessDeclContextCheck() const: Assertion `Access != AS_none && "Access specifier is AS_none inside a record decl"' failed.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0. Program arguments: /opt/compiler-explorer/clang-assertions-trunk/bin/clang++ -g -o /app/output.s -mllvm --x86-asm-syntax=intel -fno-verbose-asm -S --gcc-toolchain=/opt/compiler-explorer/gcc-snapshot -fcolor-diagnostics -fno-crash-diagnostics
1. :5:30: current parser token 'm'
2. :1:12: parsing function body 'main'
3. :1:12: in compound statement ('{}')
4. :3:5: parsing struct/union/class body '(unnamed struct at :3:5)'
#0 0x0000000004301458 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4301458)
#1 0x00000000042fe884 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x42fe884)
#2 0x0000000004243628 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
#3 0x000070ea2ea42520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
#4 0x000070ea2ea969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
#5 0x000070ea2ea42476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
#6 0x000070ea2ea287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
#7 0x000070ea2ea2871b (/lib/x86_64-linux-gnu/libc.so.6+0x2871b)
#8 0x000070ea2ea39e96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
#9 0x0000000007ba4bb8 clang::Decl::AccessDeclContextCheck() const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7ba4bb8)
#10 0x0000000007139a21 LookupDirect(clang::Sema&, clang::LookupResult&, clang::DeclContext const*) SemaLookup.cpp:0:0
#11 0x000000000713a361 clang::Sema::LookupQualifiedName(clang::LookupResult&, clang::DeclContext*, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x713a361)
#12 0x00000000071294f5 clang::Sema::CppLookupName(clang::LookupResult&, clang::Scope*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x71294f5)
#13 0x000000000712a2b5 clang::Sema::LookupName(clang::LookupResult&, clang::Scope*, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x712a2b5)
#14 0x000000000713c9a4 clang::Sema::LookupExistingLabel(clang::IdentifierInfo*, clang::SourceLocation) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x713c9a4)
#15 0x000000000713cbb5 clang::Sema::LookupOrCreateLabel(clang::IdentifierInfo*, clang::SourceLocation, clang::SourceLocation) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x713cbb5)
#16 0x0000000006aaf067 clang::Parser::ParseCastExpression(clang::CastParseKind, bool, bool&, clang::TypoCorrectionTypeBehavior, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6aaf067)
#17 0x0000000006aafd37 clang::Parser::ParseCastExpression(clang::CastParseKind, bool, clang::TypoCorrectionTypeBehavior, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6aafd37)
#18 0x0000000006aafdc9 clang::Parser::ParseAssignmentExpression(clang::TypoCorrectionTypeBehavior) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6aafdc9)
#19 0x0000000006ab43a9 clang::Parser::ParseExpression(clang::TypoCorrectionTypeBehavior) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6ab43a9)
#20 0x0000000006ab8184 clang::Parser::ParseParenExpression(clang::ParenParseOption&, bool, clang::ParenExprKind, clang::TypoCorrectionTypeBehavior, clang::OpaquePtr&, clang::SourceLocation&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6ab8184)
#21 0x0000000006aae9c8 clang::Parser::ParseCastExpression(clang::CastParseKind, bool, bool&, clang::TypoCorrectionTypeBehavior, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6aae9c8)
#22 0x0000000006aafd37 clang::Parser::ParseCastExpression(clang::CastParseKind, bool, clang::TypoCorrectionTypeBehavior, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6aafd37)
#23 0x0000000006aafdc9 clang::Parser::ParseAssignmentExpression(clang::TypoCorrectionTypeBehavior) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6aafdc9)
#24 0x0000000006ab166c clang::Parser::ParseRHSOfBinaryExpression(clang::ActionResult, clang::prec::Level) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6ab166c)
#25 0x0000000006abad0a clang::Parser::ParseConstantExpressionInExprEvalContext(clang::TypoCorrectionTypeBehavior) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6abad0a)
#26 0x0000000006abadfa clang::Parser::ParseArrayBoundExpression() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6abadfa)
#27 0x0000000006a73f19 clang::Parser::ParseBracketDeclarator(clang::Declarator&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a73f19)
#28 0x0000000006a85f13 clang::Parser::ParseDirectDeclarator(clang::Declarator&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a85f13)
#29 0x0000000006a7329f clang::Parser::ParseDeclaratorInternal(clang::Declarator&, void (clang::Parser::*)(clang::Declarator&)) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a7329f)
#30 0x000000000850d501 clang::StackExhaustionHandler::runWithSufficientStackSpace(clang::SourceLocation, llvm::function_ref) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x850d501)
#31 0x0000000006a61caf clang::Parser::ParseDeclarator(clang::Declarator&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a61caf)
#32 0x0000000006a95d75 clang::Parser::ParseCXXMemberDeclaratorBeforeInitializer(clang::Declarator&, clang::VirtSpecifiers&, clang::ActionResult&, clang::Parser::LateParsedAttrList&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a95d75)
#33 0x0000000006a9f832 clang::Parser::ParseCXXClassMemberDeclaration(clang::AccessSpecifier, clang::ParsedAttributes&, clang::Parser::ParsedTemplateInfo&, clang::ParsingDeclRAIIObject*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a9f832)
#34 0x0000000006aa14ff clang::Parser::ParseCXXClassMemberDeclarationWithPragmas(clang::AccessSpecifier&, clang::ParsedAttributes&, clang::TypeSpecifierType, clang::Decl*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6aa14ff)
#35 0x0000000006aa32bc clang::Parser::ParseCXXMemberSpecification(clang::SourceLocation, clang::SourceLocation, clang::ParsedAttributes&, unsigned int, clang::Decl*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6aa32bc)
#36 0x0000000006aa5ea0 clang::Parser::ParseClassSpecifier(clang::tok::TokenKind, clang::SourceLocation, clang::DeclSpec&, clang::Parser::ParsedTemplateInfo&, clang::AccessSpecifier, bool, clang::Parser::DeclSpecContext, clang::ParsedAttributes&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6aa5ea0)
#37 0x0000000006a78cce clang::Parser::ParseDeclarationSpecifiers(clang::DeclSpec&, clang::Parser::ParsedTemplateInfo&, clang::AccessSpecifier, clang::Parser::DeclSpecContext, clang::Parser::LateParsedAttrList*, clang::ImplicitTypenameContext) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a78cce)
#38 0x0000000006a7f337 clang::Parser::ParseSimpleDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, bool, clang::Parser::ForRangeInit*, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a7f337)
#39 0x0000000006a7f87c clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a7f87c)
#40 0x0000000006b31264 clang::Parser::ParseStatementOrDeclarationAfterAttributes(llvm::SmallVector&, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::LabelDecl*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6b31264)
#41 0x0000000006b31af6 clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector&, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::LabelDecl*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6b31af6)
#42 0x0000000006b3a43e clang::Parser::ParseCompoundStatementBody(bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6b3a43e)
#43 0x0000000006b3ac8a clang::Parser::ParseFunctionStatementBody(clang::Decl*, clang::Parser::ParseScope&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6b3ac8a)
#44 0x0000000006a40beb clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::LateParsedAttrList*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a40beb)
#45 0x0000000006a770ad clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::ParsedAttributes&, clang::Parser::ParsedTemplateInfo&, clang::SourceLocation*, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a770ad)
#46 0x0000000006a33d4b clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a33d4b)
#47 0x0000000006a3453f clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a3453f)
#48 0x0000000006a3c36a clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a3c36a)
#49 0x0000000006a3d305 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a3d305)
#50 0x0000000006a3d7b0 clang::Parser::ParseFirstTopLevelDecl(clang::OpaquePtr&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a3d7b0)
#51 0x0000000006a1e353 clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a1e353)
#52 0x0000000004c62788 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c62788)
#53 0x0000000004f58e05 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4f58e05)
#54 0x0000000004ed909e clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4ed909e)
#55 0x000000000505318d clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x505318d)
#56 0x0000000000de63ec cc1_main(llvm::ArrayRef, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xde63ec)
#57 0x0000000000ddce3a ExecuteCC1Tool(llvm::SmallVectorImpl&, llvm::ToolContext const&, llvm::IntrusiveRefCntPtr) driver.cpp:0:0
#58 0x0000000000ddcfbd int llvm::function_ref&)>::callback_fn&)>(long, llvm::SmallVectorImpl&) driver.cpp:0:0
#59 0x0000000004cd4e59 void llvm::function_ref::callback_fn>, std::__cxx11::basic_string, std::allocator>*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#60 0x0000000004243ac4 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4243ac4)
#61 0x0000000004cd546f clang::driver::CC1Command::Execute(llvm::ArrayRef>, std::__cxx11::basic_string, std::allocator>*, bool*) const (.part.0) Job.cpp:0:0
#62 0x0000000004c95f52 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c95f52)
#63 0x0000000004c96efe clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl>&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c96efe)
#64 0x0000000004c9e355 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c9e355)
#65 0x0000000000de27e1 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xde27e1)
#66 0x0000000000c8d114 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xc8d114)
#67 0x000070ea2ea29d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#68 0x000070ea2ea29e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#69 0x0000000000ddc8d5 _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xddc8d5)
clang++: error: clang frontend command failed with exit code 134 (use -v to see invocation)
Compiler returned: 134
```

Reproduce the assertion with the minimal example and inspect clang::Decl::AccessDeclContextCheck in DeclBase.cpp, then follow the label lookup path through SemaLookup.cpp and the parser frames in the stack dump. Done means the input no longer triggers an assertion and the behavior is covered by a regression test for this nested-struct array-bound case.

Written by the indexing model from the issue text.