Fix ICE on atomic enumeration type with LTO

This is a strange regression whereby an enumeration type declared as
atomic (or volatile) incorrectly triggers the ODR machinery for its
values in LTO mode.

gcc/ada/
	* gcc-interface/decl.c (gnat_to_gnu_entity): Build a TYPE_STUB_DECL
	for the main variant of an enumeration type declared as volatile.
gcc/testsuite/
	* gnat.dg/specs/lto25.ads: New test.

gcc/ada/gcc-interface/decl.c

@@ -4713,6 +4713,10 @@ gnat_to_gnu_entity (Entity_Id gnat_entity, tree gnu_expr, bool definition)
 	  const int quals
 	    = TYPE_QUAL_VOLATILE
 	      | (Is_Full_Access (gnat_entity) ? TYPE_QUAL_ATOMIC : 0);
+	  /* This is required by free_lang_data_in_type to disable the ODR.  */
+	  if (TREE_CODE (gnu_type) == ENUMERAL_TYPE)
+	    TYPE_STUB_DECL (gnu_type)
+	      = create_type_stub_decl (TYPE_NAME (gnu_type), gnu_type);
 	  gnu_type = change_qualified_type (gnu_type, quals);
 	}
 

gcc/testsuite/gnat.dg/specs/lto25.ads

@@ -0,0 +1,12 @@
+-- { dg-do compile }
+-- { dg-options "-flto" { target lto } }
+
+package Lto25 is
+
+  type Enum is (One, Two, Three) with Atomic;
+
+  type Rec is record
+    E : Enum := One;
+  end record;
+
+end Lto25;