[PATCH, i386]: Fix PR target/35553, -fkeep-inline-functions and -O errors our in SSE headers

[Uros Bizjak]

Hello!

>  >  Fixed by introducing __SSE_USE_INLINED_FUNC__ builtin define that is
>  >  defined when appropriate and by using this define through SSE headers.
>
>  Why not simply make these functions extern inline __attribute__((gnu_inline))?

Huh, indeed.

Do we need extern here or can go with static inline
__attribute__((gnu_inline, _always_inline_))

(the tests that redefine "static" won't have to be updated in this case.)

Thanks,
Uros.