use AC_PROG_FC to set Fortran compiler in configure.ac
We have to set the Fortran compiler with AC_PROG_FC in configure.ac. Otherwise libtool we run into a ugly libtool bug and get the error message
libtool: link: unsupported hardcode properties
libtool: link: See the libtool documentation for more information.
libtool: link: Fatal configuration error.if we try to compile the Fortran examples serial.