exp_dbug.ads: Document new convention for the XVZ variable.

exp_dbug.ads: Document new convention for the XVZ variable.

	* exp_dbug.ads: Document new convention for the XVZ variable.
	* gcc-interface/decl.c (gnat_to_gnu_entity) <E_Array_Type>: Generate
	debug info if necessary for the type padding the component type.
	<E_Array_Subtype>: Likewise.
	(maybe_pad_type): Emit the XVZ variable in units.
	* gcc-interface/trans.c (Loop_Statement_to_gnu): Fix formatting nits.
	(Subprogram_Body_to_gnu): Set the source line of the subprogram's node
	on statements generated to initialize the parameter attributes cache.
	Set the source line of the end label of the body on the special return
	statement built for a procedure with copy-in copy-out parameters.

From-SVN: r140513