ada: Remove dependence on secondary stack for type with controlled component

ada: Remove dependence on secondary stack for type with controlled component

There are cases where GNAT introduces a dependence on the secondary stack
in a build-in-place function with a result subtype that is definite, when
this dependence could be avoided.  In particular this is done for record
types that requires finalization due to having a controlled component.

At one time such functions required the secondary stack in order to
properly handle cases where the function might raise an exception
(to avoid improper finalization in the caller), but that is no longer
necessary.  We remove the dependence of these functions on the SS,
along with the BIPalloc formal and the generation of the big if_statement
that uses that formal.

An additional small change is to revise the condition for determining when
to generate SS mark/release within functions.

gcc/ada/ChangeLog:

	* exp_ch6.ads (Make_Build_In_Place_Call_In_Allocator): Simplify comment.
	* exp_ch6.adb (Make_Build_In_Place_Call_In_Allocator): Remove obsolete
	comment about not being able to allocate fixed-size controlled results
	on the caller side, and replace another obsolete comment with a simpler
	comment. Call Build_Allocate_Deallocate_Proc when the function doesn't
	need a BIPalloc formal to ensure that function results with controlled
	parts allocated on the caller side will be chained for finalization.
	(Make_Build_In_Place_Call_In_Object_Declaration): Call Needs_BIP_Collection
	on the function's Entity_Id rather than the function call.
	(Needs_BIP_Collection): If a BIP function doesn't need a BIPalloc formal
	then it doesn't need a BIP collection either; return False in that case.
	(Needs_BIP_Alloc_Form): Remove test of Needs_BIP_Collection.
	* exp_ch7.adb (Expand_Cleanup_Actions): Move test of Uses_Sec_Stack
	to be the first conjunct in setting of Needs_Sec_Stack_Mark, and put
	the other tests in a disjunction subsidiary to that. Improve preceding
	comment.