[Ada] Do not overwrite limited view of result type

[Ada] Do not overwrite limited view of result type

This removes obsolete code that overwrites a limited view present as the
result type of a function during the tentative analysis of prefixed
views for function calls involving tagged types. The original view is
necessary for the code generator to break the circularity present in
this setup.

The change also adds a couple of guards for the illegal case where the
limited view is the only view available when the function is invoked.

gcc/ada/

	* aspects.adb (Find_Value_Of_Aspect): Add guard.
	* sem_ch4.adb (Complete_Object_Operation): Remove obsolete code.
	* sem_ch5.adb (Has_Sec_Stack_Default_Iterator): Add guard.