LiveVariables: Do not remove dead flags from vreg operands

Also add a FIXME comment on why Mips RDDSP causes bogus dead flags to be
added which LiveVariables cleans up by accident.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@264695 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed