Revert: [RTL ifcvt] Transform (X == CST) ? -CST : Y into (X == CST) ? -X : Y when conditional negation is available

	Revert
	2016-09-30  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>

	* ifcvt.c (noce_try_avoid_const_materialization): New function.
	(noce_process_if_block): Use it.

	* gcc.target/aarch64/ifcvt_avoid_const_materialization_1.c: New test.

From-SVN: r240708