[PATCH] powerpc: Fix feraiseexcept and feclearexcept macros

[Matheus Castanho]

> __builtin_popcount (e) == 1 does not
> seem to be unreasonable to express this condition.
> 

Adhemerval and Florian, apart from the discussion to remove or not
fenvinline.h altogether, could we push this commit? This header is
currently in a broken state and I'd like to fix it for the time being.

If you have any other suggestions / reservations about using
__builtin_popcount (__e) == 1, I'd be happy to consider and provide an
alternative patch if needed.

Thanks,
Matheus Castanho