apps/libtest: add libtest demo

Redefine the name of BIN to support static library:

BIN = $(APPDIR)/libtest$(LIBEXT)

Signed-off-by: chao.an <anchao@xiaomi.com>

examples/libtest/libtest_main.c

@@ -0,0 +1,41 @@
+/****************************************************************************
+ * apps/examples/libtest/libtest_main.c
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.  The
+ * ASF licenses this file to you 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.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+#include <stdio.h>
+#include "libtest.h"
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * main
+ ****************************************************************************/
+
+int main(int argc, FAR char *argv[])
+{
+  library_test();
+  return 0;
+}