This patch fixes an issue whereby instantiations of generic packages
were incorrectly allowed despite formal and actual subprograms not
having matching declarations with anonymous constant access type
parameters.

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

-- gen1.ads

package Gen1 is
   generic
      with procedure View (IA : not null access constant Integer);
   procedure Dispatch (IA : access Integer);
end;

-- gen2.adb

package body Gen1 is
   procedure Dispatch (IA : access Integer) is
   begin
      View (IA);
   end;
end;

-- bad1.ads

with Gen1;
package Bad1 is
   procedure Bad_View (IA : not null access Integer);
   procedure Bad_Dispatch is new Gen1.Dispatch (Bad_View);
end;

-- bad1.adb

package body Bad1 is
   procedure Bad_View (IA : not null access Integer) is
   begin
      IA.all := IA.all + 1;
   end;
end;

-- gen2.ads

package Gen2 is
   generic
      with procedure View (IA : access constant Integer);
   procedure Dispatch (IA : access Integer);
end;

-- gen2.adb

package body Gen2 is
   procedure Dispatch (IA : access Integer) is
   begin
      View (IA);
   end;
end;

-- bad2.ads

with Gen2;
package Bad2 is
   procedure Bad_View (IA : access Integer);
   procedure Bad_Dispatch is new Gen2.Dispatch (Bad_View);
end;

-- bad2.adb

package body Bad2 is
   procedure Bad_View (IA : access Integer) is
   begin
      IA.all := IA.all + 1;
   end;
end;

-----------------
-- Compilation --
-----------------

$ gnatmake -q bad1.adb
$ bad1.ads:4:04: instantiation error at gen1.ads:3
$ bad1.ads:4:04: not mode conformant with declaration at line 3
$ bad1.ads:4:04: constant modifier does not match
$ gnatmake: "bad1.adb" compilation error
$ gnatmake -q bad2.adb
$ bad2.ads:4:04: instantiation error at gen2.ads:3
$ bad2.ads:4:04: not mode conformant with declaration at line 3
$ bad2.ads:4:04: constant modifier does not match
$ gnatmake: "bad2.adb" compilation error

2019-07-03  Justin Squirek  <squirek@adacore.com>

gcc/ada/

	* sem_ch6.adb (Check_Conformance): Add expression checking for
	constant modifiers in anonymous access types (in addition to
	"non-null" types) so that they are considered "matching" for
	subsequent conformance tests.

From-SVN: r272963