Define _POSIX_MONOTONIC_CLOCK and implement sysconf(_SC_MONOTONIC_CLOCK).

Bug: http://code.google.com/p/android/issues/detail?id=39680
Change-Id: I11cf10a66f9d305868a725f04f581099fb88bbfc

tests/unistd_test.cpp

@@ -0,0 +1,23 @@
+/*
+ * Copyright (C) 2012 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 <unistd.h>
+
+TEST(unistd, sysconf_SC_MONOTONIC_CLOCK) {
+  ASSERT_GT(sysconf(_SC_MONOTONIC_CLOCK), 0);
+}