No memcpy for copy ctor with -fsanitize-address-field-padding=1

Summary:
When -fsanitize-address-field-padding=1 is present
don't emit memcpy for copy constructor.
Thanks Nico for the extra test case.

Test Plan: regression tests

Reviewers: thakis, rsmith

Reviewed By: rsmith

Subscribers: rsmith, cfe-commits

Differential Revision: http://reviews.llvm.org/D6515