cmd/gc: fix confusing error when using variable as type.

Fixes #3783.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/6737053

src/cmd/gc/typecheck.c

@@ -476,7 +476,7 @@ reswitch:
 			n->left = N;
 			goto ret;
 		}
-		if(!isptr[t->etype]) {
+		if((top & Erv) && !isptr[t->etype]) {
 			yyerror("invalid indirect of %lN", n->left);
 			goto error;
 		}

test/fixedbugs/issue3783.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 foo
+
+var i int
+
+func (*i) bar() // ERROR "not a type"
+