Add -Wmodule-build to make it easy to see when modules are (re)built

Warning is default ignore, and not in -Wall.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@207975 91177308-0d34-0410-b5e6-96231b3b80d8
CodeGen: Cleanup visibility in RTTIBuilder

No functionality change.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@207978 91177308-0d34-0410-b5e6-96231b3b80d8