clang trunk: assertion "Cannot get layout of forward declarations!" in getASTRecordLayout during Sema of register asm variable with incomplete struct type

## Compiler Explorer:

- clang start crashing on `Trunk`
- generated by fuzzer

## Console
```console
clang: /root/llvm-project/llvm/tools/clang/include/clang/AST/TypeBase.h:953: const clang::ExtQualsTypeCommonBase* clang::QualType::getCommonPtr() const: Assertion `!isNull() && "Cannot retrieve a NULL type pointer"' 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. :6:17: current parser token ';'
2. :5:76: parsing function body 'void_ptr_arithmetic_test'
3. :5:76: in compound statement ('{}')
#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 0x00007928ece42520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
#4 0x00007928ece969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
#5 0x00007928ece42476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
#6 0x00007928ece287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
#7 0x00007928ece2871b (/lib/x86_64-linux-gnu/libc.so.6+0x2871b)
#8 0x00007928ece39e96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
#9 0x0000000007cd98df clang::CastExpr::CastConsistency() const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x7cd98df)
#10 0x0000000007ce32ad clang::ImplicitCastExpr::Create(clang::ASTContext const&, clang::QualType, clang::CastKind, clang::Expr*, llvm::SmallVector const*, clang::ExprValueKind, clang::FPOptionsOverride) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x7ce32ad)
#11 0x0000000006bca4c1 clang::Sema::ImpCastExprToType(clang::Expr*, clang::QualType, clang::CastKind, clang::ExprValueKind, llvm::SmallVector const*, clang::CheckedConversionKind) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x6bca4c1)
#12 0x0000000006faaf2e clang::Sema::CheckSingleAssignmentConstraints(clang::QualType, clang::ActionResult&, bool, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x6faaf2e)
#13 0x00000000070f5bf4 clang::InitializationSequence::Perform(clang::Sema&, clang::InitializedEntity const&, clang::InitializationKind const&, llvm::MutableArrayRef, clang::QualType*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x70f5bf4)
#14 0x00000000070f9362 clang::Sema::PerformCopyInitialization(clang::InitializedEntity const&, clang::SourceLocation, clang::ActionResult, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x70f9362)
#15 0x0000000007380684 clang::Sema::PerformMoveOrCopyInitialization(clang::InitializedEntity const&, clang::Sema::NamedReturnInfo const&, clang::Expr*, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x7380684)
#16 0x00000000073966b4 clang::Sema::BuildReturnStmt(clang::SourceLocation, clang::Expr*, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x73966b4)
#17 0x00000000073972a7 clang::Sema::ActOnReturnStmt(clang::SourceLocation, clang::Expr*, clang::Scope*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x73972a7)
#18 0x0000000006b2c79a clang::Parser::ParseReturnStatement() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x6b2c79a)
#19 0x0000000006b30bdd clang::Parser::ParseStatementOrDeclarationAfterAttributes(llvm::SmallVector&, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::LabelDecl*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x6b30bdd)
#20 0x0000000006b31af6 clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector&, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::LabelDecl*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x6b31af6)
#21 0x0000000006b3a43e clang::Parser::ParseCompoundStatementBody(bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x6b3a43e)
#22 0x0000000006b3ac8a clang::Parser::ParseFunctionStatementBody(clang::Decl*, clang::Parser::ParseScope&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x6b3ac8a)
#23 0x0000000006a40beb clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::LateParsedAttrList*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x6a40beb)
#24 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)
#25 0x0000000006a33d4b clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x6a33d4b)
#26 0x0000000006a3453f clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x6a3453f)
#27 0x0000000006a3c36a clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x6a3c36a)
#28 0x0000000006a3d305 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x6a3d305)
#29 0x0000000006a1e38a clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x6a1e38a)
#30 0x0000000004c62788 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x4c62788)
#31 0x0000000004f58e05 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x4f58e05)
#32 0x0000000004ed909e clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x4ed909e)
#33 0x000000000505318d clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x505318d)
#34 0x0000000000de63ec cc1_main(llvm::ArrayRef, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0xde63ec)
#35 0x0000000000ddce3a ExecuteCC1Tool(llvm::SmallVectorImpl&, llvm::ToolContext const&, llvm::IntrusiveRefCntPtr) driver.cpp:0:0
#36 0x0000000000ddcfbd int llvm::function_ref&)>::callback_fn&)>(long, llvm::SmallVectorImpl&) driver.cpp:0:0
#37 0x0000000004cd4e59 void llvm::function_ref::callback_fn>, std::__cxx11::basic_string, std::allocator>*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#38 0x0000000004243ac4 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x4243ac4)
#39 0x0000000004cd546f clang::driver::CC1Command::Execute(llvm::ArrayRef>, std::__cxx11::basic_string, std::allocator>*, bool*) const (.part.0) Job.cpp:0:0
#40 0x0000000004c95f52 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x4c95f52)
#41 0x0000000004c96efe clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl>&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x4c96efe)
#42 0x0000000004c9e355 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x4c9e355)
#43 0x0000000000de27e1 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0xde27e1)
#44 0x0000000000c8d114 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0xc8d114)
#45 0x00007928ece29d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#46 0x00007928ece29e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#47 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
```

## Code
```c
void test3(void) { *A = *B; }
void __attribute__((address_space(1))) *
^*__restrict__ __attribute__(()) __attribute__(())
__attribute__(()) __restrict _Atomic
void_ptr_arithmetic_test(void __attribute__((address_space(1))) * arg) {
return arg + 4;
}
```

Start with the supplied C reproducer and the assertion in clang/include/clang/AST/TypeBase.h:953, then trace the Sema path shown in the stack, including ImpCastExprToType and BuildReturnStmt. Done means the reproducer no longer aborts during compilation and regression coverage records the expected behavior.

Written by the indexing model from the issue text.