信号是一个内联函数，直到平台的android-21，现在是不是内联了。

signal was an inline function until platform android-21, now it's not inline anymore.

当您使用NDK R10，Android为21默认使用的，但它不是完全与运行前的Andr​​oid版本的设备复古兼容。你的情况，信号不能被您的设备上（但它会棒棒糖上正常运行）找到。

When you use the ndk r10, android-21 is used by default but it's not fully retro-compatible with devices running former Android versions. In your case, signal can't be found on your device (but it would run properly on Lollipop).

在使用NDK，你应该使用平台（ APP_PLATFORM：= Android的XX ）对应于您的安卓的minSdkVersion 。

When using the NDK, you should use the platform (APP_PLATFORM:=android-XX) that corresponds to your android:minSdkVersion.

所以在这里你可以设置 APP_PLATFORM：=机器人-15 里面的 Application.mk 的Makefile文件，你的LIB将使用信号线版本，所以不会寻找其在运行时的象征。

So here you can set APP_PLATFORM:=android-15 inside Application.mk Makefile, and your lib will use the inline version of signal, so it will not look for its symbol at runtime.