Add regression test

gcc/testsuite/
	PR ada/114593
	* gnat.dg/specs/generic_inst2-child2.ads: New test.
	* gnat.dg/specs/generic_inst2.ads: New helper.
	* gnat.dg/specs/generic_inst2-child1.ads: Likewise.

gcc/testsuite/gnat.dg/specs/generic_inst2-child1.ads

@@ -0,0 +1,17 @@
+generic
+package Generic_Inst2.Child1 is
+
+   function Get_Custom return Custom_Type;
+
+private
+
+   type Dummy is null record;
+
+   Placeholder : constant Dummy := (null record);
+
+   -- This type conversion fails (though only when
+   -- instantiated in the other package)
+   function Get_Custom return Custom_Type is 
+      (Custom_Type(Placeholder'Address));
+
+end Generic_Inst2.Child1;

gcc/testsuite/gnat.dg/specs/generic_inst2-child2.ads

@@ -0,0 +1,10 @@
+-- { dg-do compile }
+
+with Generic_Inst2.Child1;
+
+generic
+package Generic_Inst2.Child2 is
+
+   package Second is new Generic_Inst2.Child1;
+
+end Generic_Inst2.Child2;

gcc/testsuite/gnat.dg/specs/generic_inst2.ads

@@ -0,0 +1,11 @@
+private with System;
+
+package Generic_Inst2 is
+
+   type Custom_Type is private;
+
+private
+
+   type Custom_Type is new System.Address;
+
+end Generic_Inst2;