Improve preservation of FLAGS_REG mode in i386.md's peephole2s.

Improve preservation of FLAGS_REG mode in i386.md's peephole2s.

The patch tweaks several peephole2s in i386.md that propagate the flags
register, but take its mode from the SET_SRC rather than preserve the
mode of the original SET_DEST.  This encounters problems when the
SET_SRC is a VOIDmode CONST_INT.  Fixed by using match_operand with a
flags_reg_operand predicate.

2022-07-09  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	* config/i386/i386.md (define_peephole2): Use match_operand of
	flags_reg_operand to capture and preserve the mode of FLAGS_REG.
	(define_peephole2): Likewise.
	(define_peephole2): Likewise...