runtime: fix panic for make(chan [0]byte).

I suspect that this was introduced by
http://code.google.com/p/go/source/detail?r=6e4ee32fffd1

R=r
CC=golang-dev
https://golang.org/cl/4764045

src/pkg/runtime/chan.c

@@ -97,7 +97,7 @@ runtime·makechan_c(Type *elem, int64 hint)
 	int32 n;
 	byte *by;
 
-	if(hint < 0 || (int32)hint != hint || hint > ((uintptr)-1) / elem->size)
+	if(hint < 0 || (int32)hint != hint || (elem->size > 0 && hint > ((uintptr)-1) / elem->size))
 		runtime·panicstring("makechan: size out of range");
 
 	if(elem->alg >= nelem(runtime·algarray)) {

test/chan/zerosize.go

+// $G $D/$F.go && $L $F.$A && ./$A.out
+
+// Copyright 2011 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.
+
+// Making channels of a zero-sized type should not panic.
+
+package main
+
+func main() {
+	_ = make(chan [0]byte)
+	_ = make(chan [0]byte, 1)
+	_ = make(chan struct{})
+	_ = make(chan struct{}, 1)
+}