[analyzer] Warn about double-delete in C++ at the second delete...

...rather somewhere in the destructor when we try to access something and
realize the object has already been deleted. This is necessary because
the destructor is processed before the 'delete' itself.

Patch by Karthik Bhat!

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@198779 91177308-0d34-0410-b5e6-96231b3b80d8