Remember if a type has its visibility set explicitly or implicitly.
With that, centralize the way we merge visibility, always preferring explicit over
implicit and then picking the most restrictive one.
Fixes pr10113 and pr11690.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@148163 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed