[analyzer] Look through all casts when trying to track constraints.

Previously, we were losing path notes (in both text and plist form)
because the interesting DeclRefExpr was buried in a cast.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@161999 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed