match.pd: Optimize MIN_EXPR <addr1, addr2> etc. addr1 < addr2 would be simplified [PR102951]

This patch outlines the decision whether address comparison can be folded
or not from the match.pd simple comparison simplification and uses it
both there and in a new minmax simplification, such that we fold e.g.
MAX (&a[2], &a[1]) etc.
Some of the Wstringop-overflow-62.c changes might look weird, but that
seems to be mainly due to gimple_fold_builtin_memset not bothering to
copy over location, will fix that incrementally.

2021-10-28  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/102951
	* fold-const.h (address_compare): Declare.
	* fold-const.c (address_compare): New function.
	* match.pd (cmp (convert1?@2 addr@0) (convert2? addr@1)): Use
	address_compare helper.
	(minmax cmp (convert1?@2 addr@0) (convert2?@3 addr@1)): New
	simplification.

	* gcc.dg/tree-ssa/pr102951.c: New test.
	* gcc.dg/Wstringop-overflow-62.c: Adjust expected diagnostics.