[Ada] Display source code pointing at locations in messages for GNATprove

[Ada] Display source code pointing at locations in messages for GNATprove

gcc/ada/

	* errout.adb: (Error_Msg-Internal): Pass the location for a line
	insertion if any in the message.
	(Output_Messages: Add display of source code lines if -gnatdF is
	set.
	(Write_Source_Code_Line): Code clean up.
	* erroutc.adb (Prescan_Message): Apply prescan for continuation
	lines when -gnatdF is set, and record presence of line
	insertion.
	* erroutc.ads (Has_Insertion_Line): New global for prescan.
	(Error_Msg_Object): Add field to record line insertion if
	present.
	* errutil.adb (Error_Msg): Pass no location for Insertion_Sloc.