runtime: convert sigqueue to Go

LGTM=rsc
R=golang-codereviews, rsc
CC=golang-codereviews, khr
https://golang.org/cl/132090043

src/pkg/runtime/sigqueue.go

@@ -0,0 +1,42 @@
+// Copyright 2009 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.
+
+// This file implements runtime support for signal handling.
+
+package runtime
+
+func signal_recv() (m uint32) {
+	for {
+		mp := acquirem()
+		onM(&signal_recv_m)
+		ok := mp.scalararg[0] != 0
+		m = uint32(mp.scalararg[1])
+		releasem(mp)
+		if ok {
+			return
+		}
+		gonotetsleepg(&signote, -1)
+		gonoteclear(&signote)
+	}
+}
+
+func signal_enable(s uint32) {
+	mp := acquirem()
+	mp.scalararg[0] = uint(s)
+	onM(&signal_enable_m)
+	releasem(mp)
+}
+
+func signal_disable(s uint32) {
+	mp := acquirem()
+	mp.scalararg[0] = uint(s)
+	onM(&signal_disable_m)
+	releasem(mp)
+}
+
+var (
+	signal_recv_m,
+	signal_enable_m,
+	signal_disable_m mFunction
+)