We set CMAKE_Fortran_SIZEOF_DATA_PTR in the Fortran compiler information
file after detecting the compiler ABI.  However, since Fortran does not
really have pointers, the preprocessor-based detection is unreliable.
The result is needed to set CMAKE_SIZEOF_VOID_P only for Fortran-only
projects because the value can come from C or C++ compilers otherwise.
Therefore when CMAKE_SIZEOF_VOID_P is available from another language we
should defer to it.