Allow to override Asan shadow offset.

Allow to override Asan shadow offset.

2014-10-28  Yury Gribov  <y.gribov@samsung.com>

gcc/
	* asan.c (set_asan_shadow_offset): New function.
	(asan_shadow_offset): Likewise.
	(asan_emit_stack_protection): Call asan_shadow_offset.
	(build_shadow_mem_access): Likewise.
	* asan.h (set_asan_shadow_offset): Declare.
	* common.opt (fasan-shadow-offset): New option.
	(frandom-seed): Fixed parameter name.
	* doc/invoke.texi (fasan-shadow-offset): Describe new option.
	(frandom-seed): Fixed parameter name.
	* opts-global.c (handle_common_deferred_options): Handle
	-fasan-shadow-offset.
	* opts.c (common_handle_option): Likewise.

gcc/testsuite/
	* c-c++-common/asan/shadow-offset-1.c: New test.

From-SVN: r216773