LivePhysRegs: Skip reserved regs in computeLiveIns; NFCI

We do not track liveness of reserved registers so adding them to the
liveins list in computeLiveIns() was completely unnecessary.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@303937 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed