[Ada] Elaboration order v4.0 and output of dependencies

[Ada] Elaboration order v4.0 and output of dependencies

This patch adds a missing case to the mechanism that outputs the
elaboration order dependencies of units.

------------
-- Source --
------------

--  pack.ads

package Pack is
   procedure Force_Body;
end Pack;

--  pack.adb

package body Pack is
   procedure Force_Body is null;
end Pack;

--  main.adb

with Pack;

procedure Main is begin null; end Main;

----------------------------
-- Compilation and output --
----------------------------

$ gnatmake -q main.adb -bargs -e

ELABORATION ORDER DEPENDENCIES

   unit "pack (spec)" must be elaborated before unit "main (body)"
     reason: unit "main (body)" has with clause for unit "pack (spec)"
   unit "pack (spec)" must be elaborated before unit "pack (body)"
     reason: spec must be elaborated before body

2019-07-11  Hristian Kirtchev  <kirtchev@adacore.com>

gcc/ada/

	* bindo.adb: Remove the documentation of switch -d_N because it
	is no longer in use.
	* bindo-graphs.ads, bindo-graphs.adb (Is_Spec_Before_Body_Edge):
	New routine.
	* bindo-writers.adb (Write_Dependency_Edge): Add the missing
	case of a spec-before-body edge.

From-SVN: r273394