[Clang] Assertion failure in DiagnoseImmediateEscalatingReason: `FD->hasBody() && "expected the function to have a body"`

Generated by fuzzer.
Clang trunk crashed and goes back to 20.1 with -std=c++23 flag.
Compiler Explorer: https://godbolt.org/z/4T65c5x1c

Program

consteval void trigger_defect();
template < int > struct C {
public:
  static void f() {
    auto lambda = [](auto &&obj) -> decltype(0) {
      trigger_defect();
    };
    lambda(0);
  }
};
int main() {
  C<1>::f();
}

Stack Dump

<source>:8:5: error: call to immediate function 'C<1>::f()::(lambda)::operator()<int>' is not a constant expression
    8 |     lambda(0);
      |     ^
<source>:12:9: note: in instantiation of member function 'C<1>::f' requested here
   12 |   C<1>::f();
      |         ^
clang++: /root/llvm-project/llvm/tools/clang/lib/Sema/SemaDeclCXX.cpp:2604: void clang::Sema::DiagnoseImmediateEscalatingReason(clang::FunctionDecl*): Assertion `FD->hasBody() && "expected the function to have a body"' 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 -std=c++23 <source>
1.	<eof> parser at end of file
2.	<source>:4:15: instantiating function definition 'C<1>::f'
 #0 0x0000000004312838 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4312838)
 #1 0x000000000430fc94 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x430fc94)
 #2 0x00000000042528e8 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007b4caba42520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #4 0x00007b4caba969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
 #5 0x00007b4caba42476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
 #6 0x00007b4caba287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
 #7 0x00007b4caba2871b (/lib/x86_64-linux-gnu/libc.so.6+0x2871b)
 #8 0x00007b4caba39e96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
 #9 0x0000000006ebd455 (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6ebd455)
#10 0x0000000006fc94f7 clang::Sema::PopExpressionEvaluationContext() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6fc94f7)
#11 0x0000000006e5a3ca clang::Sema::ActOnFinishFunctionBody(clang::Decl*, clang::Stmt*, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6e5a3ca)
#12 0x00000000076938d6 clang::Sema::InstantiateFunctionDefinition(clang::SourceLocation, clang::FunctionDecl*, bool, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x76938d6)
#13 0x0000000007691476 clang::Sema::PerformPendingInstantiations(bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7691476)
#14 0x0000000006c10772 clang::Sema::ActOnEndOfTranslationUnitFragment(clang::TUFragmentKind) (.part.0) Sema.cpp:0:0
#15 0x0000000006c10af2 clang::Sema::ActOnEndOfTranslationUnit() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6c10af2)
#16 0x0000000006a7b845 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a7b845)
#17 0x0000000006a5c7fa clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a5c7fa)
#18 0x0000000004c7ab78 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c7ab78)
#19 0x0000000004f74f85 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4f74f85)
#20 0x0000000004ef495e clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4ef495e)
#21 0x000000000506fbfd clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x506fbfd)
#22 0x0000000000ddd1ce cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xddd1ce)
#23 0x0000000000dd3b9a ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&, llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>) driver.cpp:0:0
#24 0x0000000000dd3d1d int llvm::function_ref<int (llvm::SmallVectorImpl<char const*>&)>::callback_fn<clang_main(int, char**, llvm::ToolContext const&)::'lambda'(llvm::SmallVectorImpl<char const*>&)>(long, llvm::SmallVectorImpl<char const*>&) driver.cpp:0:0
#25 0x0000000004cee0b9 void llvm::function_ref<void ()>::callback_fn<clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#26 0x0000000004252d84 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4252d84)
#27 0x0000000004cee6cf clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const (.part.0) Job.cpp:0:0
#28 0x0000000004caf0a2 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4caf0a2)
#29 0x0000000004cb004e clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4cb004e)
#30 0x0000000004cb7495 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4cb7495)
#31 0x0000000000dd9541 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xdd9541)
#32 0x0000000000c96be4 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xc96be4)
#33 0x00007b4caba29d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#34 0x00007b4caba29e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#35 0x0000000000dd3635 _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xdd3635)
clang++: error: clang frontend command failed with exit code 134 (use -v to see invocation)
Compiler returned: 134

Reproduce the crash with the C++23 program and clang++ command shown in the issue. Start in llvm/tools/clang/lib/Sema/SemaDeclCXX.cpp around DiagnoseImmediateEscalatingReason and trace the function-instantiation path from the stack dump. Add regression coverage for this program and verify Clang reports the diagnostic without hitting the assertion.