os/signal: don't run TestTerminalSignal on Android

At least some versions of the Android libc do not define posix_openpt.

Updates #22845

Change-Id: Id21705f47ef0f9694313a7dc7351a952d48d407b
Reviewed-on: https://go-review.googlesource.com/79399
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/os/signal/internal/pty/pty.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 dragonfly freebsd linux netbsd openbsd
+// +build darwin dragonfly freebsd linux,!android netbsd openbsd
 // +build cgo
 
 // Package pty is a simple pseudo-terminal package for Unix systems,

src/os/signal/signal_cgo_test.go

@@ -2,10 +2,12 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd linux netbsd openbsd
+// +build darwin dragonfly freebsd linux,!android netbsd openbsd
 // +build cgo
 
 // Note that this test does not work on Solaris: issue #22849.
+// Don't run the test on Android because at least some versions of the
+// C library do not define the posix_openpt function.
 
 package signal_test