Do not sanitize in an abnormal context (PR sanitizer/78815).

2017-01-05  Martin Liska  <mliska@suse.cz>

	PR sanitizer/78815
	* gimplify.c (gimplify_decl_expr): Compare to
	asan_poisoned_variables instread of checking flags.
	(gimplify_target_expr): Likewise.
	(gimplify_expr): Likewise.
	(gimplify_function_tree): Conditionally initialize
	asan_poisoned_variables.

From-SVN: r244095