gc: bug241

Fixes #495.

R=ken2
CC=golang-dev
https://golang.org/cl/183156

src/cmd/gc/typecheck.c

@@ -446,7 +446,9 @@ reswitch:
 		n->op = ODOT;
 		// fall through
 	case ODOT:
-		l = typecheck(&n->left, Erv|Etype);
+		typecheck(&n->left, Erv|Etype);
+		defaultlit(&n->left, T);
+		l = n->left;
 		if((t = l->type) == T)
 			goto error;
 		if(n->right->op != ONAME) {

test/fixedbugs/bug241.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
+
+const c = 3
+var x = c.String()	// ERROR "String"
+