Fix build when targetting Android 7 or later (#14)

Support for pthread_barrier was introduced in Android 7, so trying to
build a custom implementation of that clashes with the system headers.

Author: fornwall

hidapi/libusb/hid.c

@@ -49,7 +49,7 @@
 
 #include "hidapi.h"
 
-#ifdef __ANDROID__
+#if defined(__ANDROID__) && __ANDROID_API__ < __ANDROID_API_N__
 
 /* Barrier implementation because Android/Bionic don't have pthread_barrier.
    This implementation came from Brent Priddy and was posted on