Make some changes suggested by Chris:

1. Remove the LLVM_DO_NOT_BUILD feature (not needed any more)
2. Ensure that lib/VMCore gets built first. This needs to be done because
   VMCore now uses tblgen to generate the Intrinsics header which are
   needed in other libraries. In parallel builds, this can cause problems.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@28374 91177308-0d34-0410-b5e6-96231b3b80d8