[patch]: Add check for stdint header

[Tobias Burnus]

Paolo Bonzini wrote:
> You can use GCC_STDINT_TYPES (new in this version) instead of
> GCC_HEADER_STDINT since GCC does not need int_leastNN_t and int_fastNN_t.

That is not completely true. The Fortran front end needs to know the
storage size of the int_{least,fast}*_t in order to make the
c_int_{least,fast}*_t kind parameters available in the ISO_C_BINDING
module (for interoperability with C). The size needs to match the one on
the target system in order that C and Fortran can interoperate.

I have not checked whether the change affects this (cf.
gcc/fortran/iso-c-binding.def and users of this file), but one should
check this before submittal.

Tobias