cmd/gc: fix invalid indirect error at statement level

Fixes #4429.

R=golang-dev, remyoudompheng, daniel.morsing, rsc
CC=golang-dev
https://golang.org/cl/6850097

src/cmd/gc/typecheck.c

@@ -482,7 +482,7 @@ reswitch:
 			n->left = N;
 			goto ret;
 		}
-		if((top & Erv) && !isptr[t->etype]) {
+		if((top & (Erv | Etop)) && !isptr[t->etype]) {
 			yyerror("invalid indirect of %lN", n->left);
 			goto error;
 		}

test/fixedbugs/issue4429.go

+// errorcheck
+
+// Copyright 2012 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 p
+
+type a struct {
+  a int
+}
+
+func main() {
+  av := a{};
+  *a(av); // ERROR "invalid indirect"
+}