PR 91731 - Configure error on building MPICH

[Damian Rouson]

The following is the trailing output of configuring MPICH 3.2, 3.2.1,
or 3.3.1 with the current GCC trunk:

configure: error: The Fortran compiler /opt/gnu/10.0.0/bin/gfortran
will not compile files that call the same routine with arguments of
different types.

I got the same message when I configured in a way that passes gfortran
the -fallow-argument-mismatch argument enabled by the patch posted at
https://gcc.gnu.org/ml/fortran/2019-08/msg00118.html so I assume that
patch hasn't hit the trunk yet. Does GCC 9 have the same issue.  If
so, could the patch be backported to the 9 branch after it is
committed to the trunk?  Also, is the above error message indicative
of non-standard code in MPICH?  If so, I'll submit an issue to the
MPICH developers.

Damian