cmake: add -fallow-argument-mismatch if MPICH is detected with GCC 10+

[dev-zero]

until pmodels/mpich#4300 is solved we need to add -fallow-argument-mismatch when building our MPI wrapper. The most portable and clean solution would be to try_compile a snippet triggering the issue when gcc 10+ is used and if it is triggered, add the flag. The other option would be to unconditionally add the flag when MPICH and gcc 10+ are used. The latter has the disadvantage that we manually have to update the check once MPICH resolves the issue