Summary:
Useful for figuring out with people which version they built with. We can just ask for --caffe2_version gflag or get core.build_options from python.
Also adds CMAKE_INSTALL_RPATH_USE_LINK_PATH - without it wasn't building on my Mac. How should it be tested?
Closes https://github.com/caffe2/caffe2/pull/1271
Reviewed By: bddppq
Differential Revision: D5940750
Pulled By: dzhulgakov
fbshipit-source-id: 45b4c94f67e79346a10a65b34f40fd258295dad1