i386: Add peephole2 patterns to improve subtract with borrow with memory destination...

i386: Add peephole2 patterns to improve subtract with borrow with memory destination [PR79173]

This patch adds subborrow<mode> alternative so that it can have memory
destination and adds various peephole2s which help to match it.

2023-06-15  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/79173
	* config/i386/i386.md (subborrow<mode>): Add alternative with
	memory destination and add for it define_peephole2
	TARGET_READ_MODIFY_WRITE/-Os patterns to prefer using memory
	destination in these patterns.