[clang][OpenMP] Assertion `!R.isInvalid() && "operation was asserted to never fail!"' failed.

Reproducer:
https://godbolt.org/z/W18aGsxMW
```cpp
void foo() {
#pragma omp unroll partial
for (int i = {0}; i < 2; i++)
;
}
```

Backtrace:
```console
clang++: /root/llvm-project/llvm/tools/clang/include/clang/Sema/Ownership.h:276: clang::Expr* clang::AssertSuccess(clang::ExprResult): Assertion `!R.isInvalid() && "operation was asserted to never fail!"' failed.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace and dumped files.
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 -fopenmp
1. :5:1: current parser token '}'
2. :1:12: parsing function body 'foo'
3. :1:12: in compound statement ('{}')
#0 0x000000000437c168 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x437c168)
#1 0x0000000004378fa4 llvm::sys::RunSignalHandlers() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4378fa4)
#2 0x00000000043795c4 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x43795c4)
#3 0x00000000042b4af8 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
#4 0x000077d899845330 (/lib/x86_64-linux-gnu/libc.so.6+0x45330)
#5 0x000077d89989eb2c pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x9eb2c)
#6 0x000077d89984527e raise (/lib/x86_64-linux-gnu/libc.so.6+0x4527e)
#7 0x000077d8998288ff abort (/lib/x86_64-linux-gnu/libc.so.6+0x288ff)
#8 0x000077d89982881b (/lib/x86_64-linux-gnu/libc.so.6+0x2881b)
#9 0x000077d89983b517 (/lib/x86_64-linux-gnu/libc.so.6+0x3b517)
#10 0x0000000007406e13 (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7406e13)
#11 0x00000000075205c0 clang::SemaOpenMP::ActOnOpenMPUnrollDirective(llvm::ArrayRef, clang::Stmt*, clang::SourceLocation, clang::SourceLocation) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x75205c0)
#12 0x00000000074a4b90 clang::SemaOpenMP::ActOnOpenMPExecutableDirective(llvm::omp::Directive, clang::DeclarationNameInfo const&, llvm::omp::Directive, llvm::ArrayRef, clang::Stmt*, clang::SourceLocation, clang::SourceLocation) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x74a4b90)
#13 0x0000000006d0f5ce clang::Parser::ParseOpenMPExecutableDirective(clang::Parser::ParsedStmtContext, llvm::omp::Directive, clang::SourceLocation, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6d0f5ce)
#14 0x0000000006d1c1b7 clang::Parser::ParseOpenMPDeclarativeOrExecutableDirective(clang::Parser::ParsedStmtContext, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6d1c1b7)
#15 0x0000000006d3bee4 clang::Parser::ParseStatementOrDeclarationAfterAttributes(llvm::SmallVector&, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::LabelDecl*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6d3bee4)
#16 0x0000000006d3d749 clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector&, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::LabelDecl*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6d3d749)
#17 0x0000000006d45f6e clang::Parser::ParseCompoundStatementBody(bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6d45f6e)
#18 0x0000000006d4678a clang::Parser::ParseFunctionStatementBody(clang::Decl*, clang::Parser::ParseScope&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6d4678a)
#19 0x0000000006c4a603 clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::LateParsedAttrList*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6c4a603)
#20 0x0000000006c81913 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+++0x6c81913)
#21 0x0000000006c3db4b clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6c3db4b)
#22 0x0000000006c3e34f clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6c3e34f)
#23 0x0000000006c45e11 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6c45e11)
#24 0x0000000006c46d45 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6c46d45)
#25 0x0000000006c47130 clang::Parser::ParseFirstTopLevelDecl(clang::OpaquePtr&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6c47130)
#26 0x0000000006c27bc3 clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6c27bc3)
#27 0x0000000004e6ab58 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4e6ab58)
#28 0x00000000051a1688 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x51a1688)
#29 0x000000000511e8cd clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x511e8cd)
#30 0x00000000052a179d clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x52a179d)
#31 0x0000000000e214ff cc1_main(llvm::ArrayRef, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xe214ff)
#32 0x0000000000e17eba ExecuteCC1Tool(llvm::SmallVectorImpl&, llvm::ToolContext const&, llvm::IntrusiveRefCntPtr) driver.cpp:0:0
#33 0x0000000000e1803d int llvm::function_ref&)>::callback_fn&)>(long, llvm::SmallVectorImpl&) driver.cpp:0:0
#34 0x0000000004edd539 void llvm::function_ref::callback_fn>, std::__cxx11::basic_string, std::allocator>*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#35 0x00000000042b4f34 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x42b4f34)
#36 0x0000000004eddb86 clang::driver::CC1Command::Execute(llvm::ArrayRef>, std::__cxx11::basic_string, std::allocator>*, bool*) const (.part.0) Job.cpp:0:0
#37 0x0000000004e9a062 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4e9a062)
#38 0x0000000004e9b00e clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl>&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4e9b00e)
#39 0x0000000004ea3215 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4ea3215)
#40 0x0000000000e1d8ec clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xe1d8ec)
#41 0x0000000000cc173a main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcc173a)
#42 0x000077d89982a1ca (/lib/x86_64-linux-gnu/libc.so.6+0x2a1ca)
#43 0x000077d89982a28b __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2a28b)
#44 0x0000000000e17955 _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xe17955)
clang++: error: clang frontend command failed due to signal (use -v to see invocation)
Compiler returned: 134
```

Run the supplied C++ reproducer with -fopenmp using an assertions-enabled clang, then inspect clang::SemaOpenMP::ActOnOpenMPUnrollDirective and the AssertSuccess call in tools/clang/include/clang/Sema/Ownership.h. Trace why this OpenMP unroll form produces an invalid expression; done means the reproducer no longer asserts and has regression coverage for the diagnostic or successful compilation behavior.

Written by the indexing model from the issue text.