[Ada] Implement RM C.6(19) clause entirely in the front-end

[Ada] Implement RM C.6(19) clause entirely in the front-end

2019-12-16  Eric Botcazou  <ebotcazou@adacore.com>

gcc/ada/

	* exp_ch6.adb (Requires_Atomic_Or_Volatile_Copy): New predicate.
	(Expand_Actuals): Use it to decide whether to add call by copy
	code as per the RM C.6(19) clause.
	* fe.h (Is_Atomic_Object): Remove.
	(Is_Volatile_Object): Likewise.
	* sem_util.ads (Is_Atomic_Object): Remove WARNING note.
	(Is_Volatile_Object): Likewise.
	* gcc-interface/trans.c (atomic_or_volatile_copy_required_p): Delete.
	(Call_to_gnu): Do not implement the  RM C.6(19) clause.

From-SVN: r279414