[clang] assertion failure at clang::LookupResult::isAcceptableSlow with "-std=c++20"

https://godbolt.org/z/jbrd7q7z3

The following code:

```cpp
struct D {
friend bool operator==(const D&, const D&) = default; // expected-note {{previous}}
}
export module foo:bar;
struct TestD {
friend constexpr bool operator==(const D&, const D&); // expected-error {{non-constexpr}}
bool operator==(const G&, const G&);
}
```

Resulted in this output:
```
/tmp/test.cpp:3:2: error: expected ';' after struct
3 | }
| ^
| ;
/tmp/test.cpp:4:8: error: module declaration must occur at the start of the translation unit
4 | export module foo:bar;
| ^
/tmp/test.cpp:1:1: note: add 'module;' to the start of the file to introduce a global module fragment
1 | struct D {
| ^
/tmp/test.cpp:6:25: error: 'operator==' is missing exception specification 'noexcept'
6 | friend constexpr bool operator==(const D&, const D&); // expected-error {{non-constexpr}}
| ^
| noexcept
/tmp/test.cpp:2:15: note: previous declaration is here
2 | friend bool operator==(const D&, const D&) = default; // expected-note {{previous}}
| ^
/tmp/test.cpp:7:23: error: unknown type name 'G'
7 | bool operator==(const G&, const G&);
| ^
/tmp/test.cpp:7:33: error: unknown type name 'G'
7 | bool operator==(const G&, const G&);
| ^
clang++: /home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-project/clang/lib/Sema/SemaLookup.cpp:1854: static bool clang::LookupResult::isAcceptableSlow(clang::Sema&, clang::NamedDecl*, clang::Sema::AcceptableKind): Assertion `DeclModule && "hidden decl has no owning module"' 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: /home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang++ -S -o /dev/null -O3 -std=c++20 /tmp/test.cpp
1. /tmp/test.cpp:7:36: current parser token ';'
2. /tmp/test.cpp:5:1: parsing struct/union/class body 'TestD'
Stack dump without symbol names (ensure you have llvm-symbolizer in your PATH or set the environment var `LLVM_SYMBOLIZER_PATH` to point to it):
0 clang++ 0x0000563e502ae0f9 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 121
1 clang++ 0x0000563e502aadcc llvm::sys::RunSignalHandlers() + 76
2 clang++ 0x0000563e502ab678 llvm::sys::CleanupOnSignal(unsigned long) + 216
3 clang++ 0x0000563e501edf88
4 libc.so.6 0x00007f6b69b0a520
5 libc.so.6 0x00007f6b69b5e9fc pthread_kill + 300
6 libc.so.6 0x00007f6b69b0a476 raise + 22
7 libc.so.6 0x00007f6b69af07f3 abort + 211
8 libc.so.6 0x00007f6b69af071b
9 libc.so.6 0x00007f6b69b01e96
10 clang++ 0x0000563e5317b94f clang::LookupResult::isAcceptableSlow(clang::Sema&, clang::NamedDecl*, clang::Sema::AcceptableKind) + 591
11 clang++ 0x0000563e5317dfcf clang::LookupResult::isAvailableForLookup(clang::Sema&, clang::NamedDecl*) + 47
12 clang++ 0x0000563e531996e6
13 clang++ 0x0000563e53186c5b
14 clang++ 0x0000563e53187c0b clang::Sema::CppLookupName(clang::LookupResult&, clang::Scope*) + 3659
15 clang++ 0x0000563e531885c6 clang::Sema::LookupName(clang::LookupResult&, clang::Scope*, bool, bool) + 1910
16 clang++ 0x0000563e52e5468f clang::Sema::HandleDeclarator(clang::Scope*, clang::Declarator&, llvm::MutableArrayRef) + 575
17 clang++ 0x0000563e52f05621 clang::Sema::ActOnCXXMemberDeclarator(clang::Scope*, clang::AccessSpecifier, clang::Declarator&, llvm::MutableArrayRef, clang::Expr*, clang::VirtSpecifiers const&, clang::InClassInitStyle) + 1057
18 clang++ 0x0000563e52ab17ba clang::Parser::ParseCXXClassMemberDeclaration(clang::AccessSpecifier, clang::ParsedAttributes&, clang::Parser::ParsedTemplateInfo&, clang::ParsingDeclRAIIObject*) + 5706
19 clang++ 0x0000563e52ab3230 clang::Parser::ParseCXXClassMemberDeclarationWithPragmas(clang::AccessSpecifier&, clang::ParsedAttributes&, clang::TypeSpecifierType, clang::Decl*) + 1296
20 clang++ 0x0000563e52ab38f8 clang::Parser::ParseCXXMemberSpecification(clang::SourceLocation, clang::SourceLocation, clang::ParsedAttributes&, unsigned int, clang::Decl*) + 1144
21 clang++ 0x0000563e52ab64ff clang::Parser::ParseClassSpecifier(clang::tok::TokenKind, clang::SourceLocation, clang::DeclSpec&, clang::Parser::ParsedTemplateInfo&, clang::AccessSpecifier, bool, clang::Parser::DeclSpecContext, clang::ParsedAttributes&) + 8191
22 clang++ 0x0000563e52a85732 clang::Parser::ParseDeclarationSpecifiers(clang::DeclSpec&, clang::Parser::ParsedTemplateInfo&, clang::AccessSpecifier, clang::Parser::DeclSpecContext, clang::LateParsedAttrList*, clang::ImplicitTypenameContext) + 2994
23 clang++ 0x0000563e52a40e88 clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) + 200
24 clang++ 0x0000563e52a4192f clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) + 959
25 clang++ 0x0000563e52a4d7a1 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) + 977
26 clang++ 0x0000563e52a4e7df clang::Parser::ParseTopLevelDecl(clang::OpaquePtr&, clang::Sema::ModuleImportState&) + 575
27 clang++ 0x0000563e52a2b70a clang::ParseAST(clang::Sema&, bool, bool) + 586
28 clang++ 0x0000563e50fa4071 clang::FrontendAction::Execute() + 65
29 clang++ 0x0000563e50f2dc65 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) + 1589
30 clang++ 0x0000563e5107fea3 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) + 467
31 clang++ 0x0000563e4ec82c96 cc1_main(llvm::ArrayRef, char const*, void*) + 7046
32 clang++ 0x0000563e4ec78a2a
33 clang++ 0x0000563e4ec78bbf
34 clang++ 0x0000563e50cb535d
35 clang++ 0x0000563e501ee3a0 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref) + 160
36 clang++ 0x0000563e50cb61b3
37 clang++ 0x0000563e50c6b987 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const + 167
38 clang++ 0x0000563e50c701e0 clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl>&, bool) const + 304
39 clang++ 0x0000563e50c7de44 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl>&) + 404
40 clang++ 0x0000563e4ec7e2d3 clang_main(int, char**, llvm::ToolContext const&) + 7267
41 clang++ 0x0000563e4ebd07a1 main + 113
42 libc.so.6 0x00007f6b69af1d90
43 libc.so.6 0x00007f6b69af1e40 __libc_start_main + 128
44 clang++ 0x0000563e4ec78055 _start + 37
clang++: error: clang frontend command failed due to signal (use -v to see invocation)
clang version 24.0.0git (https://github.com/llvm/llvm-project.git aefba88f46a6e55645c848f58f6ba56944d5ae62)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin
Build config: +assertions
clang++: note: diagnostic msg:
********************

PLEASE ATTACH THE FOLLOWING CRASH REPRODUCER FILES TO THE BUG REPORT:
clang++: note: diagnostic msg: /tmp/test-282301.cpp
clang++: note: diagnostic msg: /tmp/test-282301.sh
clang++: note: diagnostic msg:

********************
Aborted (core dumped)

```

To reproduce:
```
/home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang++ -std=c++20 ./test.cpp
```

Compiler version:
```
clang version 24.0.0git (https://github.com/llvm/llvm-project.git aefba88f46a6e55645c848f58f6ba56944d5ae62)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin
Build config: +assertions
```

*This bug was found by [fusion-fuzz](https://github.com/fusion-fuzz/fusion-fuzz)*

Reproduce the crash with clang++ -std=c++20 using the reduced source in the issue, then inspect clang/lib/Sema/SemaLookup.cpp at LookupResult::isAcceptableSlow and the lookup call stack. Use the attached reproducer and diagnostic output to investigate the hidden declaration lacking an owning module; done means the input no longer triggers the assertion and has a regression test.

Written by the indexing model from the issue text.