When rewriting defs and uses after spilling, don't set the weight of a

When rewriting defs and uses after spilling, don't set the weight of a
live interval to infinity if the instruction being rewritten is an
original remat def instruction.  We were only checking against the clone
of the remat def which doesn't actually appear in the IR at all.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51440 91177308-0d34-0410-b5e6-96231b3b80d8