ada: Only build access-to-subprogram wrappers when expander is active

ada: Only build access-to-subprogram wrappers when expander is active

For access-to-subprogram types with Pre/Post aspects we create a wrapper
routine that evaluates these aspects. Spec of this wrapper was created
always, while its body was only created when expansion was enabled.

Now we only create these wrappers when expansion is enabled. In
particular, we don't create them in GNATprove mode; instead, GNATprove
picks the Pre/Post expressions directly from the aspects.

gcc/ada/

	* exp_ch3.adb
	(Build_Access_Subprogram_Wrapper_Body): Build wrapper body if requested
	by routine that builds wrapper spec.
	* sem_ch3.adb
	(Analyze_Full_Type_Declaration): Only build wrapper when expander is
	active.
	(Build_Access_Subprogram_Wrapper):
	Remove special-case for GNATprove.