Use typedef for Fortran character length argument
Use typedef for Fortran character length argument

According to gcc docs, newer versions of gcc use size_t for character
length argument, whereas older versions use int.  Adapated a
pre-processor snippet from the gcc docs to define fortran_charlen_t as
size_t for GNUC>7 and int otherwise.

mcfarljm/fortwrap,mcfarljm/fortwrap,mcfarljm/fortwrap,mcfarljm/fortwrap