diagnostic.h has a couple of macros (diagnostic_last_module_changed
and diagnostic_set_last_module) which are only used within
diagnostic_report_current_module.

This patch eliminates the macros in favor of static functions within
diagnostic.c.

No functional change intended.

gcc/ChangeLog:
	* diagnostic.c (last_module_changed_p): New function.
	(set_last_module): New function.
	(diagnostic_report_current_module): Convert macro usage to
	the above functions.
	* diagnostic.h (diagnostic_context::last_module): Strengthen
	from const line_map * to const line_map_ordinary *.
	(diagnostic_last_module_changed): Delete macro.
	(diagnostic_set_last_module): Delete macro.

From-SVN: r247664