Runtime support for CFI

Control Flow Integrity support in bionic.

General design:
http://clang.llvm.org/docs/ControlFlowIntegrityDesign.html#shared-library-support

This CL implements subsections "CFI Shadow" and "CFI_SlowPath" in the above document.

Bug: 22033465
Test: bionic device tests
Change-Id: I14dfea630de468eb5620e7f55f92b1397ba06217