[Ada] Fix spurious error on limited view with incomplete type

[Ada] Fix spurious error on limited view with incomplete type

The problem is that Install_Limited_With_Clause does not fully implement
AI05-0129, in the case where a regular with clause is processed before a
limited_with clause of the same package: the visible "shadow" entity is
that of the incomplete type, instead of that of the full type per the AI.

This requires adjusting Remove_Limited_With_Unit to match the change in
Install_Limited_With_Clause and also Build_Incomplete_Type_Declaration,
which is responsible for synthesizing incomplete types out of full type
declarations for self-referential types.

A small tweak is also needed in Analyze_Subprogram_Body_Helper to align
it with an equivalent processing for CW types in Find_Type_Name. And the
patch also changes the Incomplete_View field in full type declarations
to point to the entity of the view instead of its declaration.

gcc/ada/

	* exp_ch3.adb (Build_Assignment): Adjust to the new definition of
	Incomplete_View field.
	* sem_ch10.ads (Decorate_Type): Declare.
	* sem_ch10.adb (Decorate_Type): Move to library level.
	(Install_Limited_With_Clause): In the already analyzed case, also
	deal with incomplete type declarations present in the sources and
	simplify the replacement code.
	(Build_Shadow_Entity): Deal with swapped views in package body.
	(Restore_Chain_For_Shadow): Deal with incomplete type declarations
	present in the sources.
	* sem_ch3.adb (Analyze_Full_Type_Declaration): Adjust to the new
	definition of Incomplete_View field.
	(Build_Incomplete_Type_Declaration): Small consistency tweak.
	Set the incomplete type as the Incomplete_View of the full type.
	If the scope is a package with a limited view, build a shadow
	entity for the incomplete type.
	* sem_ch6.adb (Analyze_Subprogram_Body_Helper): When replacing
	the limited view of a CW type as designated type of an anonymous
	access return type, get to the CW type of the incomplete view of
	the tagged type, if any.
	(Collect_Primitive_Operations): Adjust to the new definition of
	Incomplete_View field.
	* sinfo.ads (Incomplete_View): Denote the entity itself instead
	of its declaration.
	* sem_util.adb: Remove call to Defining_Entity.