go.crypto/ssh/terminal: enable freebsd build

syscall.Termios, which was the only thing breaking the build, is
available in go tip now
(https://code.google.com/p/go/source/detail?r=873d664b00ec)

R=golang-codereviews, bradfitz
CC=golang-codereviews
https://golang.org/cl/51690043

ssh/terminal/util.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build linux,!appengine darwin
+// +build linux,!appengine darwin freebsd
 
 // Package terminal provides support functions for dealing with terminals, as
 // commonly found on UNIX systems.

ssh/terminal/util_bsd.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin
+// +build darwin freebsd
 
 package terminal