[analyzer] Teach ConstraintManager to ignore NonLoc <> NonLoc comparisons.

These aren't generated by default, but they are needed when either side of
the comparison is tainted.

Should fix our internal buildbot.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@177846 91177308-0d34-0410-b5e6-96231b3b80d8