Build system changes to use TableGen to generate the various

Build system changes to use TableGen to generate the various
diagnostics. This builds on the patch that Sebastian committed and
then revert. Major differences are:

  - We don't remove or use the current ".def" files. Instead, for now,
    we just make sure that we're building the ".inc" files.
  - Fixed CMake makefiles to run TableGen and build the ".inc" files
    when needed. Tested with both the Xcode and Makefile generators
    provided by CMake, so it should be solid.
  - Fixed normal makefiles to handle out-of-source builds that involve
    the ".inc" files.

I'll send a separate patch to the list with Sebastian's changes that
eliminate the use of the .def files.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@67058 91177308-0d34-0410-b5e6-96231b3b80d8