core: POWER7 has a relaxed (weak) memory model

Link: https://github.com/GeneAssembly/biosal/issues/787
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
core: fix compilation error on Blue Gene/Q

Link: https://github.com/GeneAssembly/biosal/issues/786
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>