Bug#990290: petsc: add support for 64-bit integer lapack/blas

[Drew Parsons]

Source: petsc
Followup-For: Bug #990290
X-Debbugs-Cc: Giacomo Mulas <giacomo.mulas at inaf.it>

Grazie per il tuo lavoro, Giacomo.

Would you be able to provide a patch for your changes, i.e. a diff
file?  The simplest way might be to clone the git repo
(https://salsa.debian.org/science-team/petsc) and use `git diff`.

Step by step other components of the numerical library stack are
getting 64-bit support added (Hypre is the most recent upgrade), so a
diff will help identify the key changes we need to make for the BLAS
integers you need, relative to the other 64-bit that are in progress.

You might want to work from petsc 3.15, which is currently in the
debian experimental branch (I'm about to update it now)

Drew