set FFLAGS not F77FLAGS in configure env
set FFLAGS not F77FLAGS in configure env

Issue introduced in aa375e5. The environment variable corresponding to
f77 cannot be derived by upper-casing it.

Closes: #108
See: https://trac.macports.org/ticket/57358

danchr/macports-base,macports/macports-base,danchr/macports-base,macports/macports-base,neverpanic/macports-base,neverpanic/macports-base