[PATCH] Fortran: detect signaling NaNs on targets without issignaling macro in libc

[FX]

Hi Jakub,

> This doesn't seem to handle the powerpc* IBM double double long double.

Do we support the IEEE Fortran modules on this target, despite having a non-IEEE long double? I remember we talked about it when I first implemented it, but can’t remember what choice we ended up making.


> __LDBL_IS_IEC_60559__ isn't defined for this type, because it is far from
> an IEEE754 type, but it has signaling NaNs - as can be seen in glibc
> libc/sysdeps/ieee754/ldbl-128ibm/s_issignalingl.c
> the type is a pair of doubles and whether it is a sNaN or qNaN is determined
> by whether the first double is a sNaN or qNaN.
> 
> Ok for trunk?

It doesn’t hurt to provide an implementation, in any case. OK to push, and thanks for the patch.

FX