PR c/68473: sanitize source range-printing within certain macro expansions

PR c/68473: sanitize source range-printing within certain macro expansions

gcc/ChangeLog:
	PR c/68473
	* diagnostic-show-locus.c (layout::layout): Make loc_range const.
	Sanitize the layout_range against ranges that finish before they
	start.

gcc/testsuite/ChangeLog:
	PR c/68473
	* gcc.dg/plugin/diagnostic-test-expressions-1.c (fminl): New decl.
	(TEST_EQ): New macro.
	(test_macro): New function.
	* gcc.target/i386/pr68473-1.c: New test case.

From-SVN: r231919