Silence -Wpsabi warning on ARM for drcachesim.

Created by: fhahn

GCC 6+ has a warning for an ABI change due to a bug introduced in GCC 5: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=77728.

As we are building all of drcachesim and not linking to other C++ code, we can just ignore it.