[fortran,patch] Handle infinities and NaNs in intrinsics code generation

[Tobias Burnus]

Hi FX,

FX wrote:
> After the compile-time simplification, this patch fixes the handling of special values
> (infinities and NaNs) by intrinsics EXPONENT, FRACTION, SPACING, RRSPACING & SET_EXPONENT

> Bootstrapped and regtested on x86_64-linux.
> OK to commit?

Looks good to me. Thanks for taking care of F2003's IEEE support.

Tobias

PS: You might want to browse through the current (F2008 + corrigenda
+ first F2015 additions) draft at http://j3-fortran.org/doc/year/14/14-007r2.pdf

See especially the list at the beginning under the item
"Changes to the intrinsic modules IEEE_ARITHMETIC, IEEE_EXCEPTIONS, and
IEEE_FEATURES for conformance with ISO/IEC/IEEE 60559:2011: [...]"
and then later in that file.

Everthing which is in the draft is very likely to be in the final version but
of course not guranteed to be so.