gc: handle go print() and go println()

Fixes #1952.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/4611041

src/cmd/gc/walk.c

@@ -243,7 +243,16 @@ walkstmt(Node **np)
 		break;
 
 	case OPROC:
-		walkexpr(&n->left, &n->ninit);
+		switch(n->left->op) {
+		case OPRINT:
+		case OPRINTN:
+			walkexprlist(n->left->list, &n->ninit);
+			n->left = walkprint(n->left, &n->ninit, 1);
+			break;
+		default:
+			walkexpr(&n->left, &n->ninit);
+			break;
+		}
 		break;
 
 	case ORETURN:

test/golden.out

@@ -21,6 +21,9 @@ panic: runtime error: hash of unhashable type []int
 printing: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
 42 true false true +1.500000e+000 world 0x0 [0/0]0x0 0x0 0x0 255
 
+=========== ./goprint.go
+42 true false true +1.500000e+000 world 0x0 [0/0]0x0 0x0 0x0 255
+
 =========== ./helloworld.go
 hello, world
 

test/goprint.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.
+
+package main
+
+import "time"
+
+func main() {
+	go println(42, true, false, true, 1.5, "world", (chan int)(nil), []int(nil), (map[string]int)(nil), (func())(nil), byte(255))
+	time.Sleep(1e6)
+}