Make genmatch transform failure handling more consistent

Make genmatch transform failure handling more consistent

Currently whether a fail during the transform stage is fatal or
whether following patterns are still considers is a bit random
depending on whether the pattern is wrapped in a for for example.
The follwing makes it consistent by replacing early returns with
gotos to the end of the pattern processing.

2020-08-05  Richard Biener  <rguenther@suse.de>

	* genmatch.c (fail_label): New global.
	(expr::gen_transform): Branch to fail_label instead of
	returning.  Fix indent of call argument checking.
	(dt_simplify::gen_1): Compute and emit fail_label, branch
	to it instead of returning early.