Trivial commit to force LLVM to run TableGen for Mips target after

a change to the AsmMatcherEmitter, and should fix the buildbot
failure on llvm-clang-x86_64-expensive-checks-win.

The issue is also described here:
http://lists.llvm.org/pipermail/llvm-dev/2017-December/119617.html

llvm-svn: 321170