don't use MPI_THREAD_MULTIPLE because it is not tested well

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
system: add stack backtrace generator (uses glibc)

If glibc is not used, this feature does nothing.

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>