re PR tree-optimization/67815 (Optimize const1 * copysign (const2, y) into copysign (const1 * const2, y) if const1 > 0 or -copysign (const1 * const2, y) if const1 < 0)

	PR tree-optimization/67815
	* tree-ssa-reassoc.c (attempt_builtin_copysign): New function.
	(reassociate_bb): Call it.

	* gcc.dg/tree-ssa/reassoc-39.c: New test.
	* gcc.dg/tree-ssa/reassoc-40.c: New test.
	* gcc.dg/tree-ssa/reassoc-41.c: New test.

From-SVN: r228809