Log Message:
arpack-ng: fix build with gfortran 10

gfortran 10 rejects certain argument mismatches, causing build
errors. This issue is fixed upstream[0], but the commit modifies
40 files, so until the next release use -fallow-argument-mismatch
to downgrade these to warnings, as suggested by the gcc 10 porting
guide[1].

[0] \ 
https://github.com/opencollab/arpack-ng/commit/9418632214acf6d387896ab29a8f5bdff2d4e38a
[1] https://gcc.gnu.org/gcc-10/porting_to.html#argument-mismatch