Diagnostic for module importation

Diagnostic for module importation

This tweaks the 'included from ...' printing to deal with imports in
the 'include' path.  One new thing is that there can now be two
'include' names on a single line.  For example 'in module X, included
at Y'.  This reads better than placing them on different lines.

	gcc/
	* diagnostic.c (diagnostic_report_current_module): Adjust for C++
	module importation.