added missing hidapi stuff for os/2 with libusb

include/SDL_config_os2.h

@@ -38,8 +38,14 @@
 #define SDL_VIDEO_DRIVER_DUMMY 1
 #define SDL_VIDEO_DRIVER_OS2 1
 #define SDL_JOYSTICK_OS2 1
+#ifndef HAVE_LIBUSB_H  /* see Makefile */
 #define SDL_HIDAPI_DISABLED 1
 /*#undef SDL_JOYSTICK_HIDAPI */
+#else
+#define SDL_JOYSTICK_HIDAPI 1
+/* dynamically loaded libusb-1.0 dll: */
+#define SDL_LIBUSB_DYNAMIC "usb100.dll"
+#endif
 /*#undef SDL_JOYSTICK_VIRTUAL */
 
 /* Enable OpenGL support */