[patch,libgomp] Make libgomp Fortran modules multilib-aware

[FX]

> Why?  It should look for it first in 32/finclude, sure, but if not found,
> should fall back to finclude dir, where it is found.
> Does it differ between 32-bit and 64-bit compilation?

Module files are target- and ABI-dependent and can differ between multilibs. Thus gfortran only looks for intrinsic .mod files in the 32/finclude, and not the parent. This was the design choice made when we introduced them (the driver passes the one and only valid finclude directory to the compiler through the -fintrinsic-modules-path option.)

So, the best practice is for libgomp to store its .mod files into the multilib-specific finclude directory, just like libgfortran does.

FX