Fix a use of uninitialized value. OldCC is set when IsCmpZero || IsSwapped and read...

Fix a use of uninitialized value. OldCC is set when IsCmpZero || IsSwapped and read when ShouldUpdateCC || IsSwapped, and ShouldUpdateCC is independent. Fixes PR19932, but no test since I wasn't able to get any symptoms to appear, not even with valgrind and the testcase from the PR. It's clear what happened from inspection of the code.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210168 91177308-0d34-0410-b5e6-96231b3b80d8