[PATCH 4/5][Arm] New pattern for CSNEG instructions

[PATCH 4/5][Arm] New pattern for CSNEG instructions

This patch adds a new pattern, *thumb2_csneg, for generating CSNEG
instructions. It also restricts *if_neg_move and *thumb2_negscc to only match
if !TARGET_COND_ARITH which prevents undesirable matches during ifcvt.

gcc/ChangeLog:

	* config/arm/thumb2.md (*thumb2_csneg): New.
	(*thumb2_negscc): Don't match if TARGET_COND_ARITH.
	* config/arm/arm.md (*if_neg_move): Don't match if TARGET_COND_ARITH.

gcc/testsuite/ChangeLog:

	* gcc.target/arm/csneg.c: New test.

Co-authored-by: Omar Tahir <omar.tahir@arm.com>