[CMake] clang_tblgen: Use add_public_tablegen_target.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@201973 91177308-0d34-0410-b5e6-96231b3b80d8
[CMake] Resurrect mis-dropped dependency to ClangDriverOptions since r201842.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@201978 91177308-0d34-0410-b5e6-96231b3b80d8