Bug#940664: combblas FTCBFS: uses mpicc

[Drew Parsons]

Source: combblas
Followup-For: Bug #940664

There's an issue raised in the mpicc bug report #919308 for scotch
which needs to be addressed before we can take action.

pkg-config is not a complete replacement for mpicc, or at least there
is a discrepancy in the flags generated:

$ mpicc -showme:link
-pthread -L/usr/lib/x86_64-linux-gnu/openmpi/lib -lmpi

$ pkg-config --libs mpi-c
-L/usr/lib/x86_64-linux-gnu/openmpi/lib -lmpi

Without or without -pthread?  mpicc seems to think it's important to
link with -pthread.