[RTL-ifcvt] Improve conditional select ops on immediates

[RTL-ifcvt] Improve conditional select ops on immediates

	* ifcvt.c (noce_try_store_flag_constants): Make logic of the case
	when diff == STORE_FLAG_VALUE or diff == -STORE_FLAG_VALUE more
	explicit.  Prefer to add the flag whenever possible.
	(noce_process_if_block): Try noce_try_store_flag_constants before
	noce_try_cmove.

	* gcc.target/aarch64/csel_bfx_1.c: New test.
	* gcc.target/aarch64/csel_imms_inc_1.c: Likewise.

From-SVN: r226491