[analyzer] Teach trackNullOrUndef to look through ternary operators

Allows the suppression visitors trigger more often.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@177137 91177308-0d34-0410-b5e6-96231b3b80d8
[analyzer] Refactor checks in IDC visitor for consistency and speed

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@177138 91177308-0d34-0410-b5e6-96231b3b80d8