[CMake] Use correct visibility for linked libraries in CMake

When linking library dependencies, we shouldn't need to export linked
libraries to dependents. We should be explicit about this in
target_link_libraries, otherwise other targets that depend on these such
as sanitizers get repeated (and possibly even conflicting) dependencies.

Differential Revision: https://reviews.llvm.org/D57456

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@352654 91177308-0d34-0410-b5e6-96231b3b80d8