[Ada] Crash in class-wide pre/postconditions

[Ada] Crash in class-wide pre/postconditions

gcc/ada/

	* contracts.adb (Restore_Original_Selected_Component): New
	subprogram that traverses a preanalyzed expression searching for
	dispatching calls to functions whose original node was a
	selected component, and replacing them with their original node.
	This functionality is required because the preanalyis of
	dispatching calls using the Object.Operation notation transforms
	such calls, and we need the original condition to properly
	inherit and extend the condition expression on tagged type
	derivations.  This functionality was previously provided by the
	routine Install_Original_Selected_Component (as part of
	inheriting conditions); now it is performed as part of the
	preanalysis of the condition, thus avoiding repeatedly
	installing and restoring such nodes.
	(Install_Original_Selected_Component): Removed.
	(Restore_Dispatching_Calls): Removed.