os: create sys_bsd.go

R=rsc
CC=golang-dev
https://golang.org/cl/897042
diff --git a/src/pkg/os/sys_bsd.go b/src/pkg/os/sys_bsd.go
new file mode 100644
index 0000000..188993b
--- /dev/null
+++ b/src/pkg/os/sys_bsd.go
@@ -0,0 +1,19 @@
+// 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.
+
+// os code shared between *BSD systems including OS X (Darwin)
+// and FreeBSD.
+
+package os
+
+import "syscall"
+
+func Hostname() (name string, err Error) {
+	var errno int
+	name, errno = syscall.Sysctl("kern.hostname")
+	if errno != 0 {
+		return "", NewSyscallError("sysctl kern.hostname", errno)
+	}
+	return name, nil
+}