Fixed some issues that resulted in erroneous duplicate symbol error messages.

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@189228 91177308-0d34-0410-b5e6-96231b3b80d8
Updated the main comment with respect to problems and future directions.

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@189229 91177308-0d34-0410-b5e6-96231b3b80d8