clang crashes instead of diagnosing error when a non-type template parameter of a CRTP base's member template has a type that depends on the incomplete derived class

clang crashes in CodeGen on programs that should be rejected with a clean diagnostic.

```c++
template
struct enable_if {};
template <>
struct enable_if { using type = int; };

template
struct integral_constant { static constexpr T value = V; };

template
struct Trait : integral_constant {};

template
struct CRTP
{
template ::value>::type = 0>
void fn() const {}
};

struct Derived : CRTP
{
static constexpr bool flag = true;
};

void f()
{
Derived d;
d.fn();
}
```

```
:15:59: error: internal error: could not emit constant value "abstractly"
15 | template ::value>::type = 0>
| ^
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-trunk/bin/clang++ -g -o /app/output.s -fno-verbose-asm -S -target aarch64-linux-gnu --gcc-toolchain=/opt/compiler-explorer/arm64/gcc-15.2.0/aarch64-unknown-linux-gnu --sysroot=/opt/compiler-explorer/arm64/gcc-15.2.0/aarch64-unknown-linux-gnu/aarch64-unknown-linux-gnu/sysroot -fcolor-diagnostics -fno-crash-diagnostics -std=c++20
1. parser at end of file
2. Per-file LLVM IR generation
3. :16:10: Generating code for declaration 'CRTP::fn'
#0 0x0000000003cc7fd8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3cc7fd8)
#1 0x0000000003cc591c llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3cc591c)
#2 0x0000000003c08798 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
#3 0x000076d744c45330 (/lib/x86_64-linux-gnu/libc.so.6+0x45330)
#4 0x000000000439922b clang::CodeGen::CodeGenTypes::ConvertTypeForMem(clang::QualType) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x439922b)
#5 0x0000000004142327 clang::CodeGen::CodeGenModule::EmitNullConstant(clang::QualType) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4142327)
#6 0x000000000414d14a clang::CodeGen::ConstantEmitter::emitAbstract(clang::Expr const*, clang::QualType) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x414d14a)
#7 0x00000000040a50b8 clang::CodeGen::CGDebugInfo::CollectTemplateParams(std::optional, llvm::DIFile*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x40a50b8)
#8 0x00000000040b04c0 clang::CodeGen::CGDebugInfo::collectFunctionDeclProps(clang::GlobalDecl, llvm::DIFile*, llvm::StringRef&, llvm::StringRef&, llvm::DIScope*&, llvm::MDTupleTypedArrayWrapper&, llvm::DINode::DIFlags&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x40b04c0)
#9 0x00000000040b0e6a clang::CodeGen::CGDebugInfo::emitFunctionStart(clang::GlobalDecl, clang::SourceLocation, clang::SourceLocation, clang::QualType, llvm::Function*, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x40b0e6a)
#10 0x00000000042eb123 clang::CodeGen::CodeGenFunction::StartFunction(clang::GlobalDecl, clang::QualType, llvm::Function*, clang::CodeGen::CGFunctionInfo const&, clang::CodeGen::FunctionArgList const&, clang::SourceLocation, clang::SourceLocation) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x42eb123)
#11 0x00000000042efd95 clang::CodeGen::CodeGenFunction::GenerateCode(clang::GlobalDecl, llvm::Function*, clang::CodeGen::CGFunctionInfo const&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x42efd95)
#12 0x000000000434655a clang::CodeGen::CodeGenModule::EmitGlobalFunctionDefinition(clang::GlobalDecl, llvm::GlobalValue*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x434655a)
#13 0x000000000433fba4 clang::CodeGen::CodeGenModule::EmitGlobalDefinition(clang::GlobalDecl, llvm::GlobalValue*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x433fba4)
#14 0x000000000434e05f clang::CodeGen::CodeGenModule::EmitDeferred() (/opt/compiler-explorer/clang-trunk/bin/clang+++0x434e05f)
#15 0x00000000043513c3 clang::CodeGen::CodeGenModule::Release() (/opt/compiler-explorer/clang-trunk/bin/clang+++0x43513c3)
#16 0x00000000046a8dbe (anonymous namespace)::CodeGeneratorImpl::HandleTranslationUnit(clang::ASTContext&) ModuleBuilder.cpp:0:0
#17 0x00000000046a671d clang::BackendConsumer::HandleTranslationUnit(clang::ASTContext&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x46a671d)
#18 0x0000000006328fbc clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x6328fbc)
#19 0x00000000046a73e5 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-trunk/bin/clang+++0x46a73e5)
#20 0x00000000049e0671 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-trunk/bin/clang+++0x49e0671)
#21 0x0000000004972e35 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4972e35)
#22 0x0000000004ab322b clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4ab322b)
#23 0x0000000000dcb258 cc1_main(llvm::ArrayRef, char const*, void*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0xdcb258)
#24 0x0000000000dc309b ExecuteCC1Tool(llvm::SmallVectorImpl&, llvm::ToolContext const&, llvm::IntrusiveRefCntPtr) driver.cpp:0:0
#25 0x0000000000dc313d int llvm::function_ref&)>::callback_fn&)>(long, llvm::SmallVectorImpl&) driver.cpp:0:0
#26 0x0000000004722e59 void llvm::function_ref::callback_fn>, std::__cxx11::basic_string, std::allocator>*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#27 0x0000000003c08b53 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3c08b53)
#28 0x000000000472389d clang::driver::CC1Command::Execute(llvm::ArrayRef>, std::__cxx11::basic_string, std::allocator>*, bool*) const (.part.0) Job.cpp:0:0
#29 0x00000000046dda72 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-trunk/bin/clang+++0x46dda72)
#30 0x00000000046e1dd5 clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl>&, bool) const (/opt/compiler-explorer/clang-trunk/bin/clang+++0x46e1dd5)
#31 0x00000000046ed16c clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl>&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x46ed16c)
#32 0x0000000000dc7bd1 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0xdc7bd1)
#33 0x0000000000d0e20a main (/opt/compiler-explorer/clang-trunk/bin/clang+++0xd0e20a)
#34 0x000076d744c2a1ca (/lib/x86_64-linux-gnu/libc.so.6+0x2a1ca)
#35 0x000076d744c2a28b __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2a28b)
#36 0x0000000000dc2b45 _start (/opt/compiler-explorer/clang-trunk/bin/clang+++0xdc2b45)
clang++: error: clang frontend command failed due to signal (use -v to see invocation)
Compiler returned: 139
```

https://godbolt.org/z/cvzMYxhdW

According to `[temp.inst]`, implicit instantiation of a class template specialization causes the implicit instantiation of the declarations, but not of the definitions, of the non-deleted class member functions. clang should reject the code as instantiation of `Trait`, triggered by evaluating `Trait::value` as part of instantiating `fn`'s declaration, fails. However, compilation proceeds as if the program were well formed until it crashes later in CodeGen.