[cleanup] Fix another place where we were including the tablegen'ed code
of a '.inc' file before including actual headers. In this case we had
both duplicated a header's include and were including a standard header.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206840 91177308-0d34-0410-b5e6-96231b3b80d8