c-family: Implement -Warray-compare [PR97573]

c-family: Implement -Warray-compare [PR97573]

This patch addresses one of my leftovers from GCC 11.  C++20 introduced
[depr.array.comp]: "Equality and relational comparisons between two operands
of array type are deprecated." so this patch adds -Warray-compare.  Since the
code in question is dubious (the comparison doesn't actually compare the array
elements), I've added this warning for C too, and enabled it in all C++ modes.

	PR c++/97573

gcc/c-family/ChangeLog:

	* c-common.h (do_warn_array_compare): Declare.
	* c-warn.c (do_warn_array_compare): New.
	* c.opt (Warray-compare): New option.

gcc/c/ChangeLog:

	* c-typeck.c (parser_build_binary_op): Call do_warn_array_compare.

gcc/cp/ChangeLog:

	* typeck.c (cp_build_binary_op): Call do_warn_array_compare.

gcc/ChangeLog:

	* doc/invoke.texi: Document -Warray-compare.

gcc/testsuite/ChangeLog:

	* c-c++-common/Warray-compare-1.c: New test.
	* c-c++-common/Warray-compare-2.c: New test.