Allow asan at -O0

Allow asan at -O0

This patch defines a new asan pass gate that is activated at -O0, in
addition to the pass that was initially activated at -O3 level The
patch also does some comment cleanups here and there.

	* asan.c (build_check_stmt): Rename join_bb variable to else_bb.
	(gate_asan_O0): New function.
	(pass_asan_O0): New variable.
	* passes.c (init_optimization_passes): Add pass_asan_O0.
	* tree-pass.h (pass_asan_O0): New declaration.

From-SVN: r193435