The compiler can crash when compiling the prefixed form of subprogram
calls for untagged types when extensions are enabled. Problems can also
manifest in cases where such calls occur in the absence of extensions
being enabled.  The source of this is that the
Direct_Primitive_Operations lists were conditionally being initialized,
based on whether extensions are allowed or whether untagged types are
involved. This set of changes is directed at making the lists be
unconditionally initialized and inherited in most cases (note that there
might still be some missing cases).

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

	* sem_ch3.adb (Analyze_Full_Type_Declaration): If the full type
	has a primitives list but its base type doesn't, set the base
	type's list to the full type's list (covers certain constrained
	cases, such as for arrays).
	(Analyze_Incomplete_Type_Decl): Unconditionally initialize an
	incomplete type's primitives list.
	(Analyze_Subtype_Declaration): Unconditionally set a subtype's
	primitives list to the base type's list, so the lists are
	shared.
	(Build_Derived_Private_Type): Unconditionally initialize a
	derived private type's list to a new empty list.
	(Build_Derived_Record_Type): Unconditionally initialize a
	derived record type's list to a new empty list (now a single
	call for tagged and untagged cases).
	(Derived_Type_Declaration): Unconditionally initialize a derived
	type's list to a new empty list in error cases (when Parent_Type
	is undefined or illegal).
	(Process_Full_View): Unconditionally copy the primitive
	operations from the private view to the full view (rather than
	conditioning it on whether extensions are enabled).
	* sem_ch7.adb (New_Private_Type): Unconditionally initialize an
	untagged private type's primitives list to a new empty list.