[Ada] Ada_2020 AI12-0220 Pre/Postconditions on Access_To_Subprogram types

[Ada] Ada_2020 AI12-0220 Pre/Postconditions on Access_To_Subprogram types

2020-06-17  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* sem_ch3.adb (Analyze_Full_Type_Declaration): For an
	access_to_subprogram declaration that has aspect specifications,
	call Build_Access_ Subprogram_Wrapper at once, so that pre- and
	postcondition aspects are analyzed in the context of a
	subprogram declaration.
	(Build_Access_Subprogram_Wrapper): Examine aspect specifications
	of an Access_To_Subprogram declaration. If pre- or
	postconditions are declared for it, create declaration for
	subprogram wrapper and add the corresponding aspect
	specifications to it. Replace occurrences of the type name by
	that of the generated subprogram, so that attributes 'Old and
	'Result can appear in a postcondition.
	* exp_ch3.adb (Build_Access_Subprogram_Wrapper_Body): Moved
	here from sem_prag.adb.
	* exp_ch3.ads (Build_Access_Subprogram_Wrapper_Body): Visible
	subprogram.
	* sem_prag.adb (Build_Access_Subprogram_Wrapper / _Body): Moved
	to sem_ch3.adb and exp_ch3.adb.