[dev.garbage] all: merge dev.cc into dev.garbage

The garbage collector is now written in Go.
There is plenty to clean up (just like on dev.cc).

all.bash passes on darwin/amd64, darwin/386, linux/amd64, linux/386.

TBR=rlh
R=austin, rlh, bradfitz
CC=golang-codereviews
https://golang.org/cl/173250043

src/runtime/lfstack.go

@@ -0,0 +1,36 @@
+// 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.
+
+// Lock-free stack.
+// The following code runs only on g0 stack.
+
+package runtime
+
+import "unsafe"
+
+func lfstackpush(head *uint64, node *lfnode) {
+	node.pushcnt++
+	new := lfstackPack(node, node.pushcnt)
+	for {
+		old := atomicload64(head)
+		node.next = old
+		if cas64(head, old, new) {
+			break
+		}
+	}
+}
+
+func lfstackpop(head *uint64) unsafe.Pointer {
+	for {
+		old := atomicload64(head)
+		if old == 0 {
+			return nil
+		}
+		node, _ := lfstackUnpack(old)
+		next := atomicload64(&node.next)
+		if cas64(head, old, next) {
+			return unsafe.Pointer(node)
+		}
+	}
+}