[dev.cc] runtime: convert netbsd/amd64 port to Go

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/169620043
diff --git a/src/runtime/os2_netbsd.go b/src/runtime/os2_netbsd.go
new file mode 100644
index 0000000..46576b9
--- /dev/null
+++ b/src/runtime/os2_netbsd.go
@@ -0,0 +1,18 @@
+// Copyright 2010 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 runtime
+
+const (
+	_SS_DISABLE  = 4
+	_SIG_BLOCK   = 1
+	_SIG_UNBLOCK = 2
+	_SIG_SETMASK = 3
+	_NSIG        = 33
+	_SI_USER     = 0
+
+	// From NetBSD's <sys/ucontext.h>
+	_UC_SIGMASK = 0x01
+	_UC_CPU     = 0x04
+)