platform:GFORTRAN_OSX_MACPORTS gcc-10 compilation fix

[gsnoep]

When installing GACODE using the GFORTRAN_OSX_MACPORTS platform file and instructions I ran into a fatal compilation error:

After some digging I found this was likely due to the fact macports had automatically installed gcc-10, which has stricter handling of Fortran argument types.

After reading:

• ScaLAPACK fails with GCC 10 Reference-ScaLAPACK/scalapack#21
• https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91731
• https://gcc.gnu.org/onlinedocs/gfortran/Fortran-Dialect-Options.html#Fortran-Dialect-Options

I added "-w -fallow-argument-mismatch" to the gfortran call in the platform file, which according to the documentation linked above turns any errors of mismatching between calls to external procedures and the procedure definitions into warnings, which are suppressed at the same time.

This fixed the issue for me. Since the gcc documentation strongly discourages using this option, perhaps in the future fixing the underlying issue of aligning with the stricter argument type requirements in the newer gcc might be necessary.

[jcandy]

I think you have done the right thing to add the fix to F77 (so it applies only to the legacy code). If something is complied in GACODE with F77, it typically means we are dealing with pristine legacy code, and really should not change the sources.

Maybe a less dangerous flag can be swapped in at some point.