Bug 19161

        The mopac port needs to be compiled with f2c/cc. The compiler
controller for this is provided by the f77 port. The current f77 port
installs the binary as ftn77 but the mopac port calls the older binary
name fc. People should keep their ports tree up to date and so this port
should reflect current reality.

Fix: Apply the patch below. I am not sure what to do about the case
where people update the mopac port directory but do not update the rest
of the ports tree. However, the mopac port was recently updated so it
stands to reason that if one has the updated mopac port subdirectory they
probably have a current ports tree. Thus the build dependency should be
for ftn77 rather than fc.