[libcxx-commits] [libcxx] [libc++] Simplify the implementation of std::invoke (PR #213623)

[via libcxx-commits]

higher-performance wrote:

CI is failing; I think you have some [errors with incomplete types](https://github.com/llvm/llvm-project/actions/runs/30799065119/job/91639197313?pr=213623#step:3:2965) for example:
```
  # | libcxx/test/std/concepts/concepts.callable/concept.regularinvocable/regular_invocable.compile.pass.cpp:282:53:   required from here
  # |   282 | static_assert(check_member_is_invocable<int S::*, S>());
  # |       |               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~
  # | build/generic-gcc/libcxx/test-suite-install/include/c++/v1/__type_traits/invoke.h:128:38: error: invalid use of incomplete type ‘struct S’
  # |   128 | inline const bool __is_invocable_v = __is_invocable(_Func, _Args...);
  # |       |                                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  # | libcxx/test/std/concepts/concepts.callable/concept.regularinvocable/regular_invocable.compile.pass.cpp:41:8: note: forward declaration of ‘struct S’
  # |    41 | struct S;
  # |       |        ^
```

https://github.com/llvm/llvm-project/pull/213623