[clang][OpenMP] Assertion `!isa<TagDecl>(this)' failed.

Reproducer:
https://godbolt.org/z/W8eqn6Khs
```cpp
enum omp_interop_t : long unsigned int {};

template void foo() {
T t;
#pragma omp interop init(target : t)
}

void bar(int *y) {
foo();
--y;
}
```

Backtrace:
```console
clang++: /root/llvm-project/llvm/tools/clang/include/clang/AST/Decl.h:3583: const clang::Type* clang::TypeDecl::getTypeForDecl() const: Assertion `!isa(this)' 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. parser at end of file
2. :3:28: instantiating function definition 'foo'
#0 0x000000000441d858 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x441d858)
#1 0x000000000441a704 llvm::sys::RunSignalHandlers() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x441a704)
#2 0x000000000441ad3c llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x441ad3c)
#3 0x0000000004359d18 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
#4 0x00007b7f7b845330 (/lib/x86_64-linux-gnu/libc.so.6+0x45330)
#5 0x00007b7f7b89eb2c pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x9eb2c)
#6 0x00007b7f7b84527e raise (/lib/x86_64-linux-gnu/libc.so.6+0x4527e)
#7 0x00007b7f7b8288ff abort (/lib/x86_64-linux-gnu/libc.so.6+0x288ff)
#8 0x00007b7f7b82881b (/lib/x86_64-linux-gnu/libc.so.6+0x2881b)
#9 0x00007b7f7b83b517 (/lib/x86_64-linux-gnu/libc.so.6+0x3b517)
#10 0x0000000007569982 isValidInteropVariable(clang::Sema&, clang::Expr*, clang::SourceLocation, llvm::omp::Clause) SemaOpenMP.cpp:0:0
#11 0x00000000075699e6 clang::SemaOpenMP::ActOnOpenMPInitClause(clang::Expr*, clang::OMPInteropInfo&, clang::SourceLocation, clang::SourceLocation, clang::SourceLocation, clang::SourceLocation) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x75699e6)
#12 0x00000000078d4ba2 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformOMPInitClause(clang::OMPInitClause*) SemaTemplateInstantiate.cpp:0:0
#13 0x0000000007911bf7 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformOMPExecutableDirective(clang::OMPExecutableDirective*) SemaTemplateInstantiate.cpp:0:0
#14 0x00000000079149a4 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformOMPInteropDirective(clang::OMPInteropDirective*) SemaTemplateInstantiate.cpp:0:0
#15 0x000000000790e6d5 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformCompoundStmt(clang::CompoundStmt*, bool) SemaTemplateInstantiate.cpp:0:0
#16 0x00000000079181ee clang::Sema::SubstStmt(clang::Stmt*, clang::MultiLevelTemplateArgumentList const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x79181ee)
#17 0x00000000079b69d5 clang::Sema::InstantiateFunctionDefinition(clang::SourceLocation, clang::FunctionDecl*, bool, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x79b69d5)
#18 0x00000000079b4bf6 clang::Sema::PerformPendingInstantiations(bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x79b4bf6)
#19 0x0000000006ee5942 clang::Sema::ActOnEndOfTranslationUnitFragment(clang::TUFragmentKind) (.part.0) Sema.cpp:0:0
#20 0x0000000006ee5c82 clang::Sema::ActOnEndOfTranslationUnit() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6ee5c82)
#21 0x0000000006d4688a clang::Parser::ParseTopLevelDecl(clang::OpaquePtr&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6d4688a)
#22 0x0000000006d23c12 clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6d23c12)
#23 0x0000000004f20de8 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4f20de8)
#24 0x000000000524e948 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x524e948)
#25 0x00000000051db4cd clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x51db4cd)
#26 0x000000000532337d clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x532337d)
#27 0x0000000000da9a0c cc1_main(llvm::ArrayRef, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xda9a0c)
#28 0x0000000000da062a ExecuteCC1Tool(llvm::SmallVectorImpl&, llvm::ToolContext const&, llvm::IntrusiveRefCntPtr) driver.cpp:0:0
#29 0x0000000000da07ad int llvm::function_ref&)>::callback_fn&)>(long, llvm::SmallVectorImpl&) driver.cpp:0:0
#30 0x0000000004f98d49 void llvm::function_ref::callback_fn>, std::__cxx11::basic_string, std::allocator>*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#31 0x000000000435a154 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x435a154)
#32 0x0000000004f998b5 clang::driver::CC1Command::Execute(llvm::ArrayRef>, std::__cxx11::basic_string, std::allocator>*, bool*) const (.part.0) Job.cpp:0:0
#33 0x0000000004f516d2 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4f516d2)
#34 0x0000000004f56037 clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl>&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4f56037)
#35 0x0000000004f60705 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4f60705)
#36 0x0000000000da5f0a clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xda5f0a)
#37 0x0000000000cc1dea main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcc1dea)
#38 0x00007b7f7b82a1ca (/lib/x86_64-linux-gnu/libc.so.6+0x2a1ca)
#39 0x00007b7f7b82a28b __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2a28b)
#40 0x0000000000d9ffd5 _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xd9ffd5)
clang++: error: clang frontend command failed due to signal (use -v to see invocation)
Compiler returned: 134
```

Reproduce the assertion with the linked Compiler Explorer example using clang++ and OpenMP. Start in isValidInteropVariable in SemaOpenMP.cpp, then follow the template-instantiation path through SemaTemplateInstantiate.cpp; add regression coverage for the reproducer and verify compilation no longer aborts.

Written by the indexing model from the issue text.