Build with -fvisibility=hidden
Summary:
This change changes the build to use -fvisibility=hidden
The exports this patch removes are symbols that should have never been exported
by the dylib in the first place, and should all be symbols which the linker
won't de-duplicate across SO boundaries, making them safe to remove.
After this change, we should be able to apply `_LIBCPP_HIDDEN` to the versioning namespace without changing the export lists.
Reviewers: ldionne, mclow.lists
Reviewed By: ldionne
Subscribers: smeenai, mgorny, libcxx-commits
Differential Revision: https://reviews.llvm.org/D53868
llvm-svn: 345664