[clang] Assertion `NextVal != ArgumentEnd && "Value for integer select modifier was" " larger than the number of options in the diagnostic string!"' failed.

Reproducer:
https://godbolt.org/z/Pv4ehchMx
```cpp
typedef __attribute__((ext_vector_type(4))) float float4;

float4 foo[2] = {
{1,2},
};

static_assert(foo[2][0], "");
```

Backtrace:
```console
clang++: /root/llvm-project/llvm/tools/clang/lib/Basic/Diagnostic.cpp:831: void HandleSelectModifier(const clang::Diagnostic&, unsigned int, const char*, unsigned int, llvm::SmallVectorImpl&): Assertion `NextVal != ArgumentEnd && "Value for integer select modifier was" " larger than the number of options in the diagnostic string!"' 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
1. parser at end of file
#0 0x0000000004413f18 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4413f18)
#1 0x0000000004410dc4 llvm::sys::RunSignalHandlers() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4410dc4)
#2 0x00000000044113fc llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x44113fc)
#3 0x000000000434eec8 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
#4 0x00007d25b9645330 (/lib/x86_64-linux-gnu/libc.so.6+0x45330)
#5 0x00007d25b969ec0c pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x9ec0c)
#6 0x00007d25b964527e raise (/lib/x86_64-linux-gnu/libc.so.6+0x4527e)
#7 0x00007d25b96288ff abort (/lib/x86_64-linux-gnu/libc.so.6+0x288ff)
#8 0x00007d25b962881b (/lib/x86_64-linux-gnu/libc.so.6+0x2881b)
#9 0x00007d25b963b517 (/lib/x86_64-linux-gnu/libc.so.6+0x3b517)
#10 0x00000000047cbf54 clang::Diagnostic::FormatDiagnostic(char const*, char const*, llvm::SmallVectorImpl&) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x47cbf54)
#11 0x00000000052b6506 clang::TextDiagnosticPrinter::HandleDiagnostic(clang::DiagnosticsEngine::Level, clang::Diagnostic const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x52b6506)
#12 0x00000000047c80e0 clang::DiagnosticsEngine::Report(clang::DiagnosticsEngine::Level, clang::Diagnostic const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x47c80e0)
#13 0x00000000047c87f5 clang::DiagnosticsEngine::ProcessDiag(clang::DiagnosticBuilder const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x47c87f5)
#14 0x00000000047c88d5 clang::DiagnosticsEngine::EmitDiagnostic(clang::DiagnosticBuilder const&, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x47c88d5)
#15 0x0000000006f0adb6 clang::Sema::EmitDiagnostic(unsigned int, clang::DiagnosticBuilder const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6f0adb6)
#16 0x0000000006f95672 clang::SemaBase::ImmediateDiagBuilder::~ImmediateDiagBuilder() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6f95672)
#17 0x0000000006ef2278 clang::SemaBase::SemaDiagnosticBuilder::~SemaDiagnosticBuilder() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6ef2278)
#18 0x000000000731348d clang::Sema::VerifyIntegerConstantExpression(clang::Expr*, llvm::APSInt*, clang::Sema::VerifyICEDiagnoser&, clang::AllowFoldKind) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x731348d)
#19 0x0000000007313842 clang::Sema::VerifyIntegerConstantExpression(clang::Expr*, llvm::APSInt*, unsigned int, clang::AllowFoldKind) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7313842)
#20 0x000000000721ff57 clang::Sema::BuildStaticAssertDeclaration(clang::SourceLocation, clang::Expr*, clang::Expr*, clang::SourceLocation, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x721ff57)
#21 0x0000000006dc79cb clang::Parser::ParseStaticAssertDeclaration(clang::SourceLocation&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6dc79cb)
#22 0x0000000006dbead6 clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6dbead6)
#23 0x0000000006d75530 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6d75530)
#24 0x0000000006d76445 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6d76445)
#25 0x0000000006d5281a clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6d5281a)
#26 0x0000000004f213c8 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4f213c8)
#27 0x0000000005251378 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5251378)
#28 0x00000000051dec0d clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x51dec0d)
#29 0x000000000532566d clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x532566d)
#30 0x0000000000d8fbcc cc1_main(llvm::ArrayRef, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xd8fbcc)
#31 0x0000000000d868ca ExecuteCC1Tool(llvm::SmallVectorImpl&, llvm::ToolContext const&, llvm::IntrusiveRefCntPtr) driver.cpp:0:0
#32 0x0000000000d86a4d int llvm::function_ref&)>::callback_fn&)>(long, llvm::SmallVectorImpl&) driver.cpp:0:0
#33 0x0000000004f99ee9 void llvm::function_ref::callback_fn>, std::__cxx11::basic_string, std::allocator>*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#34 0x000000000434f2c4 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x434f2c4)
#35 0x0000000004f9aa55 clang::driver::CC1Command::Execute(llvm::ArrayRef>, std::__cxx11::basic_string, std::allocator>*, bool*) const (.part.0) Job.cpp:0:0
#36 0x0000000004f525c2 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4f525c2)
#37 0x0000000004f56f27 clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl>&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4f56f27)
#38 0x0000000004f61675 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4f61675)
#39 0x0000000000d8c0ba clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xd8c0ba)
#40 0x0000000000cc9fea main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcc9fea)
#41 0x00007d25b962a1ca (/lib/x86_64-linux-gnu/libc.so.6+0x2a1ca)
#42 0x00007d25b962a28b __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2a28b)
#43 0x0000000000d86275 _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xd86275)
clang++: error: clang frontend command failed due to signal (use -v to see invocation)
Compiler returned: 134
```

Reproduce the assertion with the provided C++ snippet and inspect llvm/tools/clang/lib/Basic/Diagnostic.cpp around HandleSelectModifier at line 831. Trace how the static_assert diagnostic supplies its select-modifier arguments. Done means the reproducer no longer aborts and emits a diagnostic normally, with a regression test added if the relevant test location is identified.

Written by the indexing model from the issue text.