middle-end: expand copysign handling from lockstep to nested iters

middle-end: expand copysign handling from lockstep to nested iters

various optimizations in match.pd only happened on COPYSIGN in lock step
which means they exclude IFN_COPYSIGN.  COPYSIGN however is restricted to only
the C99 builtins and so doesn't work for vectors.

The patch expands these optimizations to work as nested iters.

This is needed for the second patch which will add the testcase.

gcc/ChangeLog:

	PR tree-optimization/109154
	* match.pd: expand existing copysign optimizations.