bootstrap/84402 - improve (match ...) code generation

bootstrap/84402 - improve (match ...) code generation

The following avoids duplicating matching code for (match ...)
in match.pd when possible.  That's more easily possible for
(match ...) than simplify because we do not need to handle
common matches (those would be diagnosed only during compiling)
nor is the result able to inspect the active operator.

Specifically this reduces the size of the generated matches for
the atomic ops as noted in PR108129.

gimple-match.cc shrinks from 245k lines to 209k lines with this patch.

	PR bootstrap/84402
	PR tree-optimization/108129
	* genmatch.cc (lower_for): For (match ...) delay
	substituting into the match operator if possible.
	(dt_operand::gen_gimple_expr): For user_id look at the
	first substitute for determining how to access operands.
	(dt_operand::gen_generic_expr): Likewise.
	(dt_node::gen_kids): Properly sort user_ids according
	to their substitutes.
	(dt_node::gen_kids_1): Code-generate user_id matching.