ada: ICE on BIP call in class-wide function return within instance

ada: ICE on BIP call in class-wide function return within instance

The compiler blows up (such as with a Storage_Error or Assert_Failure)
on a call to a limited build-in-place function occurring in the return
for a function with a limited class-wide result. Such a function
should include extra formals for a task master and activation chain
(because it's possible for a limited class-wide type to have values
with task parts), but when the enclosing function occurs within an
instantiation and the result subtype comes from a formal type, the
extra formals were missing for the enclosing function. As a result,
the attempt to retrieve the task master formal for passing along to
a BIP call in the return failed when calling Build_In_Place_Formal to
loop through the formals. When determining the need for the formals in
Create_Extra_Formals, Needs_BIP_Actual_Task_Actuals was returning False,
because Might_Have_Tasks incorrectly returned False due to the test
of Is_Limited_Record flag on the class-wide generic actual subtype's
Etype being False. Is_Limited_Record was not being properly inherited
by the class-wide type in the case of private extensions, because
Make_Class_Wide_Type was called in Analyze_Private_Extension_Declaration
before certain flags (such as Is_Limited_Record and Is_Controlled_Active)
are inherited later in Build_Derived_Record_Type (which will also call
Make_Class_Wide_Type). This is corrected by removing the early call
to Make_Class_Wide_Type.

gcc/ada/

	* exp_ch6.adb (Might_Have_Tasks): Remove unneeded Etype call from
	call to Is_Limited_Record, since that flag is now properly
	inherited by class-wide types.
	* sem_ch3.adb (Analyze_Private_Extension_Declaration): Remove call
	to Make_Class_Wide_Type, which is done too early, and will later
	be done in Build_Derived_Record_Type after flags such as
	Is_Limited_Record and Is_Controlled_Active have been set on the
	derived type.