[Analyzer] Skip symbolic regions based on conjured symbols in comparison of the conta...

[Analyzer] Skip symbolic regions based on conjured symbols in comparison of the containers of iterators

Checking whether two regions are the same is a partially decidable problem:
either we know for sure that they are the same or we cannot decide. A typical
case for this are the symbolic regions based on conjured symbols. Two
different conjured symbols are either the same or they are different. Since
we cannot decide this and want to reduce false positives as much as possible
we exclude these regions whenever checking whether two containers are the
same at iterator mismatch check.

Differential Revision: https://reviews.llvm.org/D53754

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@356049 91177308-0d34-0410-b5e6-96231b3b80d8