In commit ecd84147 (Fortran: Detect pointer size in gfortran on MinGW,
2011-11-29) we started testing for __SIZEOF_POINTER__ but not all GNU
Fortran compilers define this. Check also for __SIZEOF_SIZE_T__ which
at least one version of gfortran defines without also defining
__SIZEOF_POINTER__.
Use __SIZEOF_POINTER__ which the GNU Fortran compiler defines at least
on 64-bit MinGW. Assume default size 4 on MinGW if gfortran does not
define the size.
Implement Fortran 32/64-bit ABI detection on some platforms. We need to
set CMAKE_SIZEOF_VOID_P correctly in Fortran-only projects so that the
find_library() command knows whether to look for 64-bit binaries. We
also detect ELF binaries to enable RPATH replacement. See issue #10119.
