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