Don't suppress bogus usage of macros from system headers in -Wformat (PR c/78304)

Don't suppress bogus usage of macros from system headers in -Wformat (PR c/78304)

gcc/ChangeLog:
	PR c/78304
	* substring-locations.c (format_warning_va): Strengthen case 1 so
	that both endpoints of the substring must be within the format
	range for just the substring to be printed.

gcc/testsuite/ChangeLog:
	PR c/78304
	* gcc.dg/format/diagnostic-ranges.c (test_macro): Undef INT_FMT.
	(test_macro_2): New test.
	(test_macro_3): New test.
	(test_macro_4): New test.
	(test_non_contiguous_strings): Convert line number to line offset.
	* gcc.dg/format/pr78304-2.c: New test case.
	* gcc.dg/format/pr78304.c: New test case.

From-SVN: r244453