Initial import of asan from the Google branch

Initial import of asan from the Google branch

This patch imports the initial state of asan as it was in the
Google branch.

It provides basic infrastructure for asan to instrument memory
accesses on the heap, at -O3.  Note that it supports neither stack nor
global variable protection.

The rest of the patches of the set is intended to further improve this
base.

gcc/ChangeLog

	* Makefile.in: Add asan.c and its dependencies.
	* common.opt: Add -faddress-sanitizer option.
	* invoke.texi: Document the new flag.
	* passes.c: Add the asan pass.
	* toplev.c (compile_file): Call asan_finish_file.
	* asan.c: New file.
	* asan.h: New file.
	* tree-pass.h: Declare pass_asan.

Co-Authored-By: Diego Novillo <dnovillo@google.com>
Co-Authored-By: Dodji Seketeli <dodji@redhat.com>
From-SVN: r193432