[PATCH]: Address PR middle-end/35509 by adding a separate isinf_sign builtin

[Paolo Carlini]

Kaveh R. Ghazi ha scritto:
>> The best one I know is that all the FP_* values are passed in as extra
>> arguments to the macro.  I think that's better than building 
>> knowledge of
>> these values in particular C libraries into GCC.
> Yes I like that, I'll do it. :-)
Great! I will immediately put it to good use in the C++ library! (at 
some point in the past, we already briefly discussed this solution).

Paolo.