To update gc and libatomic_ops

cd OMCompiler/3rdParty
# make a branch
> git checkout -b update_gc_NUMBER
# get the commits for bdwgc
> git subtree pull --squash --prefix gc https://github.com/ivmai/bdwgc master
# fix any conflicts we might have
# make omc be compiled/linked only against our version of libgc:
> cd gc
> sed -i s/libgc/libomcgc/g Makefile.am configure.ac cord/cord.am
> commit the changes

# get the commits for libatomic_ops
> git subtree pull --squash --prefix gc/libatomic_ops https://github.com/ivmai/libatomic_ops master
# fix any conflicts we might have
> commit the changes

Push your changes to your local github repo:
# for OMCompiler-3rdParty in your github USER space
> git add remote USER https://github.com/USER/OMCompiler-3rdParty.git
> git push USER update_gc_NUMBER