swift234

Make sure that the sanitizers use the same minimum OS X deployment target as llvm/clang/swift.

Otherwise, we run into an issue with certain clangs and linking in libc++. libc++
in certain clangs require a minimum deployment target of at least 10.7.

I have not investigated further since I am trying to make progress on the
branching scheme.

rdar://26081474
(cherry picked from commit 2a27443f3ee63cc55e952e4cfb43c24661c4b7ca)