Remove option emitter from clang-tblgen

The CMake build was still using it because I forgot to s/CLANG/LLVM/ in
the tablegen() call.  The Makefile build is already using llvm-tblgen.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@184192 91177308-0d34-0410-b5e6-96231b3b80d8