Implement <pty.h>.

Based on the package/apps/Terminal implementation. I'll switch them over
shortly. This also lets us build the toybox version of netcat.

Change-Id: Ia922a100141a67409264b43b937eeca07b21f344

tests/utmp_test.cpp

@@ -0,0 +1,25 @@
+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <gtest/gtest.h>
+
+#include <utmp.h>
+
+TEST(utmp, login_tty) {
+  // login_tty is tested indirectly by the openpty and forkpty tests.
+  // This test just checks that we're exporting the symbol independently.
+  ASSERT_EQ(-1, login_tty(-1));
+}