[gfortran] Fix PR15175: Type mismatch with SCALE and SET_EXPONENT

[Tobias Schlüter]

Paul Brook wrote:
> No. You should be converting to whatever type is used by the library 
> implementation.  This means "int" for SCALE and "GFC_INTEGER_4" for 
> SET_EXPONENT.
> 

Thanks, of course on i686 they're all the same, so it would still do the right
thing. Ok with the checks replaced with '!= gfc_c_int_kind' and '!= 4',
respectively?

- Tobi