middle-end/80342 - genmatch optimize outer conversions

middle-end/80342 - genmatch optimize outer conversions

The following improves genmatch generated code so we avoid more
spurious SSA assignments to be pushed to the GIMPLE sequence or
simplifications rejected when we're not supposed to produce any
for outer and intermediate conversions.

	* genmatch.cc (::gen_transform): Add in_place parameter.
	Assert it isn't set in unexpected places.
	(possible_noop_convert): New.
	(expr::gen_transform): Support in_place and emit code to
	compute a child in-place when the operation is a conversion.
	(dt_simplify::gen_1): Arrange for an outermost conversion
	to be elided by generating the transform of the operand
	in-place.
	* match.pd (__real cepxi (x) -> cos (x)): Use single_use.