[Patch / RFA] Use builtins for the classification macros

[Paolo Carlini]

Paolo Carlini wrote:
> Thanks Richard. I just noticed that, with it, we get an ICE in
> expr_size, at explow.c:249 (instead of the expected error),
A bit of additional info: other facilities, like isfinite for example,
do not ICE, instead error out, as expected, saying that the type isn't
floating-point. Looks like a rather simple issue, a bit of error
checking on the type of the argument missing in the implementation of
__builtin_isnormal...

Paolo.