Fix previous commit: poison only class members, simpler tests

Summary: Poisoning applied to only class members, and before dtors for base class invoked

Implement poisoning of only class members in dtor, as opposed to also
poisoning fields inherited from base classes. Members are poisoned
only once, by the last dtor for a class. Skip poisoning if class has
no fields.
Verify emitted code for derived class with virtual destructor sanitizes
its members only once.
Removed patch file containing extraneous changes.

Reviewers: eugenis, kcc

Differential Revision: http://reviews.llvm.org/D11951


Simplified test cases for use-after-dtor

Summary: Simplified test cases to focus on one feature at time.
Tests updated to align with new emission order for sanitizing
callback.

Reviewers: eugenis, kcc

Differential Revision: http://reviews.llvm.org/D12003

llvm-svn: 244933