gc: recursive type error

Fixes #245.

R=ken2
https://golang.org/cl/164094

src/cmd/gc/align.c

@@ -205,6 +205,9 @@ dowidth(Type *t)
 		checkwidth(t->down);
 		break;
 	case TFORW:		// should have been filled in
+		yyerror("invalid recursive type %T", t);
+		w = 1;	// anything will do
+		break;
 	case TANY:
 		// dummy type; should be replaced before use.
 		if(!debug['A'])

src/cmd/gc/typecheck.c

@@ -1039,6 +1039,8 @@ reswitch:
 	case ODCLTYPE:
 		ok |= Etop;
 		typecheck(&n->left, Etype);
+		if(!incannedimport)
+			checkwidth(n->left->type);
 		goto ret;
 	}
 

test/fixedbugs/bug224.go

+// errchk $G $D/$F.go
+
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+type T T		// ERROR "recursive"
+