[gfortran] Disable "long double" real kind on mingw32

[Danny Smith]

> 
> 
> Index: config/i386/mingw32.h
> ===================================================================
> --- config/i386/mingw32.h       (revision 118930)
> +++ config/i386/mingw32.h       (working copy)
> @@ -116,3 +116,7 @@
> /* mingw32 atexit function is safe to use in shared libraries.  Use it
>      to register C++ static destructors.  */
> #define TARGET_CXX_USE_ATEXIT_FOR_CXA_ATEXIT hook_bool_void_true
> +
> +/* mingw32 doesn't have proper I/O support for long double.  */
> +#undef GFORTRAN_WITHOUT_LONGDOUBLE
> +#define GFORTRAN_WITHOUT_LONGDOUBLE 
> 

This should really be based on a configure test.  My mingw32 does 
have proper I/O support for long double because I use a homegrown
sprintf
that is ISO C99 compliant.  

Danny