[Ada] Spurious warning on elaboration issue in dead code

[Pierre-Marie de Rodat <derodat at adacore dot com>]

This patch updates the new ABE mechanism to fully remove a recorded top level
elaboration scenario from its data structures when the scenario appears in dead
code. Previously the mechanism suppressed the generation of checks for such a
scenario, but still produced warnings.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

2017-11-09  Hristian Kirtchev  <kirtchev@adacore.com>

	* sem_elab.adb: Update the documentation on adding a new elaboration
	schenario. Add new hash table Recorded_Top_Level_Scenarios.
	(Is_Check_Emitting_Scenario): Removed.
	(Is_Recorded_Top_Level_Scenario): New routine.
	(Kill_Elaboration_Scenario): Reimplemented.
	(Record_Elaboration_Scenario): Mark the scenario as recorded.
	(Set_Is_Recorded_Top_Level_Scenario): New routine.
	(Update_Elaboration_Scenario): Reimplemented.
	* sinfo.adb (Is_Recorded_Scenario): Removed.
	(Set_Is_Recorded_Scenario): Removed.
	* sinfo.ads: Remove attribute Is_Recorded_Scenario along with
	occurrences in nodes.
	(Is_Recorded_Scenario): Removed along with pragma Inline.
	(Set_Is_Recorded_Scenario): Removed along with pragma Inline.

gcc/testsuite/

2017-11-09  Hristian Kirtchev  <kirtchev@adacore.com>

	* gnat.dg/elab3.adb, gnat.dg/elab3.ads, gnat.dg/elab3_pkg.adb,
	gnat.dg/elab3_pkg.ads: New testcase.

Attachment: difs
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