This patch refactors the forced elaboration order functionality,
reintegrates it in Binde, and impelements it in Bindo.

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

--  server.ads

package Server is
end Server;

--  client.ads

with Server;

package Client is
end Client;

--  main.adb

with Client;

procedure Main is begin null; end Main;

--  duplicate_1.txt

server (spec)
client (spec)
server (spec)

--  error_unit_1.txt

no such unit
client (spec)

--  error_unit_2.txt

no such unit
client (spec)

--  error_unit_3.txt

no such unit     --  comment
client (spec)

--  error_unit_4.txt

         no such unit     --  comment

client (spec)

--  error_unit_5.txt

no such unit (body)
client (spec)

--  error_unit_6.txt

    no such unit (body)
client (spec)

--  error_unit_7.txt

    no such unit (body)    --  comment
client (spec)

--  error_unit_8.txt

    no such unit (body)--  comment
client (spec)

--  error_unit_9.txt

    no such unit--  comment
client (spec)

--  no_unit_1.txt

--  no_unit_2.txt

--  no_unit_3.txt

      --  comment

--  no_unit_4.txt

--  no_unit_5.txt

--  no_unit_6.txt

       --  comment

--  no_unit_7.txt

--  no_unit_8.txt

    --  comment
--  comment

--  ok_unit_1.txt

server (spec)
client (spec)

--  ok_unit_2.txt

    server (spec)
client (spec)

--  ok_unit_3.txt

    server (spec)
client (spec)

--  ok_unit_4.txt

    server (spec)      --  comment
client (spec)

--  ok_unit_5.txt

server (spec)
client (spec)

--  ok_unit_6.txt

server (spec)
client (spec)    --  comment

--  ok_unit_7.txt

server (spec)
client (spec)    --  comment

--  ok_unit_8.txt

    --  comment
--  comment
    server (spec)

   --  comment
--  comment

client (spec)    --  comment

--  ok_unit_9.txt

server (spec)--  comment
client (spec)

----------------------------
-- Compilation and output --
----------------------------
$ gnatmake -q main.adb
$ gnatbind -fno_unit_1.txt main.ali
$ gnatbind -fno_unit_2.txt main.ali
$ gnatbind -fno_unit_3.txt main.ali
$ gnatbind -fno_unit_4.txt main.ali
$ gnatbind -fno_unit_5.txt main.ali
$ gnatbind -fno_unit_6.txt main.ali
$ gnatbind -fno_unit_7.txt main.ali
$ gnatbind -fno_unit_8.txt main.ali
$ gnatbind -ferror_unit_1.txt main.ali
$ gnatbind -ferror_unit_2.txt main.ali
$ gnatbind -ferror_unit_3.txt main.ali
$ gnatbind -ferror_unit_4.txt main.ali
$ gnatbind -ferror_unit_5.txt main.ali
$ gnatbind -ferror_unit_6.txt main.ali
$ gnatbind -ferror_unit_7.txt main.ali
$ gnatbind -ferror_unit_8.txt main.ali
$ gnatbind -ferror_unit_9.txt main.ali
$ gnatbind -fduplicate_1.txt main.ali
$ gnatbind -fok_unit_1.txt main.ali
$ gnatbind -fok_unit_2.txt main.ali
$ gnatbind -fok_unit_3.txt main.ali
$ gnatbind -fok_unit_4.txt main.ali
$ gnatbind -fok_unit_5.txt main.ali
$ gnatbind -fok_unit_6.txt main.ali
$ gnatbind -fok_unit_7.txt main.ali
$ gnatbind -fok_unit_8.txt main.ali
$ gnatbind -fok_unit_9.txt main.ali
"no such unit": not present; ignored
"no such unit": not present; ignored
"no such unit": not present; ignored
"no such unit": not present; ignored
"no such unit%b": not present; ignored
"no such unit%b": not present; ignored
"no such unit%b": not present; ignored
"no such unit%b": not present; ignored
"no such unit": not present; ignored
server (spec) <-- client (spec)
error: duplicate_1.txt:3: duplicate unit name "server (spec)" from line 1
server (spec) <-- client (spec)
server (spec) <-- client (spec)
server (spec) <-- client (spec)
server (spec) <-- client (spec)
server (spec) <-- client (spec)
server (spec) <-- client (spec)
server (spec) <-- client (spec)
server (spec) <-- client (spec)
server (spec) <-- client (spec)

2019-07-03  Hristian Kirtchev  <kirtchev@adacore.com>

gcc/ada/

	* binde.adb: Remove with clause for System.OS_Lib.
	(Force_Elab_Order): Refactor the majority of the code in Butil.
	Use the new forced units iterator to obtain unit names.
	* bindo-builders.adb: Add with and use clauses for Binderr,
	Butil, Opt, Output, Types, GNAT, and GNAT.Dynamic_HTables.  Add
	a hash table which maps units to line number in the forced
	elaboration order file.
	(Add_Unit): New routine.
	(Build_Library_Graph): Create forced edges between pairs of
	units listed in the forced elaboration order file.
	(Create_Forced_Edge, Create_Forced_Edges, Destroy_Line_Number,
	Duplicate_Unit_Error, Hash_Unit, Internal_Unit_Info,
	Is_Duplicate_Unit, Missing_Unit_Info): New routines.
	* bindo-graphs.adb (Is_Internal_Unit, Is_Predefined_Unit):
	Refactor some of the behavior to Bindo-Units.
	* bindo-graphs.ads: Enable the enumeration literal for forced
	edges.
	* bindo-units.adb, bindo-units.ads (Is_Internal_Unit,
	Is_Predefined_Unit): New routines.
	* butil.adb: Add with and use clauses for Opt, GNAT, and
	System.OS_Lib.  Add with clause for Unchecked_Deallocation.
	(Has_Next, Iterate_Forced_Units, Next, Parse_Next_Unit_Name,
	Read_Forced_Elab_Order_File): New routines.
	* butil.ads: Add with and use clauses for Types.  Add new
	iterator over the units listed in the forced elaboration order
	file.
	(Has_Next, Iterate_Forced_Units, Next): New routine.
	* namet.adb, namet.ads (Present): New routine.

From-SVN: r272987