[Ada] Suppression of elaboration-related warnings

[Ada] Suppression of elaboration-related warnings

This patch modifies the effects of pragma Warnings (Off, ...) to suppress
elaboration warnings related to an entity.

2018-05-23  Hristian Kirtchev  <kirtchev@adacore.com>

gcc/ada/

	* einfo.adb (Is_Elaboration_Checks_OK_Id): Use predicate
	Is_Elaboration_Target.
	(Is_Elaboration_Target): New routine.
	(Is_Elaboration_Warnings_OK_Id): Use predicate Is_Elaboration_Target.
	(Set_Is_Elaboration_Checks_OK_Id): Use predicate Is_Elaboration_Target.
	(Set_Is_Elaboration_Warnings_OK_Id): Use predicate
	Is_Elaboration_Target.
	* einfo.ads: Add new synthesized attribute Is_Elaboration_Target along
	with occurrences in nodes.
	(Is_Elaboration_Target): New routine.
	* sem_prag.adb (Analyze_Pragma): Suppress elaboration warnings when an
	elaboration target is subject to pragma Warnings (Off, ...).

gcc/testsuite/

	* gnat.dg/elab5.adb, gnat.dg/elab5_pkg.adb, gnat.dg/elab5_pkg.ads: New
	testcase.

From-SVN: r260580