Draft: d/rules: Work around missing mpi-c.pc on 32-bit by falling back to mpi.pc
Closes: #1103970
/cc @stapelberg @helmutg @zeha
This is a fairly crude workaround for #1102928 which could be applied if mpich isn't fixed soon, in order to get valgrind to migrate. Builds successfully for amd64 and i386 in sbuild (schroot mode, in a bookworm VM), otherwise untested.
It would probably be better to adjust Helmut's patch as I suggested in https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1103970#10, but I haven't tried that yet - I wanted to do this proof-of-concept and make sure it worked, before investing time in fighting with Autoconf!