[X86] Move HasNOPL to a subtarget feature bit. Plumb MCSubtargetInfo through the MCAsmBackend constructor

After D41349, we can no get a MCSubtargetInfo into the MCAsmBackend constructor. This allows us to get NOPL from a subtarget feature rather than a CPU name blacklist.

Differential Revision: https://reviews.llvm.org/D41721

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@322227 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed