This script can be used by CI systems to test things like availability
markup and binary compatibility on older MacOS versions. This is still
a bit rough on the edges, for example we don't test libc++abi yet.
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@350752 91177308-0d34-0410-b5e6-96231b3b80d8
