Hide .version directives in assembly code on Mac, since XCode doesn't
seem to like them.  Patch from Rhys Kidd (rhyskidd@gmail.com).
Fixes #339688.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14623 a5019735-40e9-0310-863c-91ae7b9d1cf9