Some minor HONOR_NANS improvements to match.pd

Some minor HONOR_NANS improvements to match.pd

Tweak the constant folding of X CMP X in when X can't be a NaN.

2022-03-16  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	* match.pd (X CMP X -> true): Test tree_expr_maybe_nan_p
	instead of HONOR_NANS.
	(X LTGT X -> false): Enable if X is not tree_expr_maybe_nan_p, as
	this can't trap/signal.