[Bug bootstrap/97163] Build error with -mcpu=power9 on ppc64

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97163

--- Comment #3 from Segher Boessenkool <segher at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #2)
> Guess we need something like:
> -#elif defined(_ARCH_PWR8) && defined(__ALTIVEC__)
> +#elif (GCC_VERSION >= 4005) && defined(_ARCH_PWR8) && defined(__ALTIVEC__)
> in libcpp/lex.c if clang doesn't support the altivec attribute and the
> builtins.

But it should!  What is actually going wrong here?  The compiler should
not declare it supports what is tested for by __ALTIVEC__ if it doesn't.