cdefs.h sometimes used names like __glibc_clang_has_attribute and
sometimes __glibc_has_attribute. There is no need in glibc or
Gnulib to distinguish clang from other compilers here, so be
consistent and use the simpler names.
* lib/cdefs.h (__glibc_has_builtin, __glibc_has_extension):
Rename from __glibc_clang_has_builtin, __glibc_clang_has_extension.
All uses changed.
(__glibc_clang_has_attribute): Remove. All uses replaced
by __glibc_has_attribute.
* lib/libc-config.h [!__glibc_likely]: Undef them here too.
This fixes a problem where __glibc_has_attribute was not undeffed.