[libc++][NFC] Remove __has_keyword

[philnik]

Summary

has_keyword is almost not used anymore. There are only two cases. One can be replaced by has_builtin and the other seems entirely redundant, so we can remove the definition.

[Mordante]

libcxx/include/__config

1155

Why is this NFC?

[philnik]

libcxx/include/__config

1155

Because this is always false for GCC and always true for Clang.

[Mordante]

LGTM!

[hubert.reinterpretcast]

libcxx/include/__config

1155

This is not NFC: -std=gnu++98 -pedantic-errors has this evaluate to false for Clang.

https://godbolt.org/z/xsfvhEfz9

[hubert.reinterpretcast]

This causes #include <algorithm> to fail with -std=gnu++98 -pedantic-errors:

$ clang++ -xc++ -<<<'#include <algorithm>' -std=gnu++98 -pedantic-errors 2>&1 | sed 's#/.*/bin#/bin#;' | head -n 20
In file included from <stdin>:1:
In file included from /bin/../include/c++/v1/algorithm:1811:
In file included from /bin/../include/c++/v1/__algorithm/pstl_any_all_none_of.h:12:
In file included from /bin/../include/c++/v1/__algorithm/pstl_find.h:14:
In file included from /bin/../include/c++/v1/__algorithm/pstl_backend.h:12:
In file included from /bin/../include/c++/v1/__algorithm/pstl_backends/cpu_backend.h:49:
In file included from /bin/../include/c++/v1/__algorithm/pstl_backends/cpu_backends/any_of.h:15:
In file included from /bin/../include/c++/v1/__atomic/atomic.h:12:
In file included from /bin/../include/c++/v1/__atomic/atomic_base.h:12:
In file included from /bin/../include/c++/v1/__atomic/atomic_sync.h:12:
In file included from /bin/../include/c++/v1/__atomic/contention_t.h:12:
/bin/../include/c++/v1/__atomic/cxx_atomic_impl.h:816:28: error: no template named '__cxx_atomic_base_impl'
  816 |           typename _Base = __cxx_atomic_base_impl<_Tp> >
      |                            ^
In file included from <stdin>:1:
In file included from /bin/../include/c++/v1/algorithm:1811:
In file included from /bin/../include/c++/v1/__algorithm/pstl_any_all_none_of.h:12:
In file included from /bin/../include/c++/v1/__algorithm/pstl_find.h:14:
In file included from /bin/../include/c++/v1/__algorithm/pstl_backend.h:12:
In file included from /bin/../include/c++/v1/__algorithm/pstl_backends/cpu_backend.h:49:
Return:  0x00:0   Thu Sep  7 14:34:31 2023 EDT

[xingxue]

I've reverted this patch to unblock the internal AIX buildbot.

[Mordante]

In D158215#4641153, @xingxue wrote:

I've reverted this patch to unblock the internal AIX buildbot.

Thanks! This should at least not be NFC. Since it breaks things I think we should abandon this patch.
At least the new information should be taken into account for the review.