Fix ICE with -g and -std=c23 when forming composite types [PR113438]

Set TYPE_STUB_DECL to an artificial decl when creating a new structure
as a composite type.

	PR c/113438

gcc/c/
	* c-typeck.cc (composite_type_internal): Set TYPE_STUB_DECL.

gcc/testsuite/
	* gcc.dg/pr113438.c: New test.

gcc/c/c-typeck.cc

@@ -585,6 +585,11 @@ composite_type_internal (tree t1, tree t2, struct composite_cache* cache)
 	  /* Setup the struct/union type.  Because we inherit all variably
 	     modified components, we can ignore the size expression.  */
 	  tree expr = NULL_TREE;
+
+	  /* Set TYPE_STUB_DECL for debugging symbols.  */
+	  TYPE_STUB_DECL (n) = pushdecl (build_decl (input_location, TYPE_DECL,
+						     NULL_TREE, n));
+
 	  n = finish_struct(input_location, n, fields, attributes, NULL, &expr);
 
 	  n = qualify_type (n, t1);

gcc/testsuite/gcc.dg/pr113438.c

@@ -0,0 +1,7 @@
+/* PR113438
+ * { dg-do compile }
+ * { dg-options "-std=c23 -g" } */
+
+void g(struct foo { int x; } a);
+void g(struct foo { int x; } a);
+