Reapply "Make NumMicroOps a variable in the subtarget's instruction itinerary."

Reapplies r159406 with minor cleanup. The regressions appear to have been spurious.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159541 91177308-0d34-0410-b5e6-96231b3b80d8
9 files changed