Needed to fix PR18303 to correctly re-encode the instruction if it
is relaxed.
We keep a copy of the MCSubtargetInfo to make sure that we are not
effected by future changes to the subtarget info coming from the
assembler (e.g. when parsing .code 16 directived).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200347 91177308-0d34-0410-b5e6-96231b3b80d8