Don't build SDL_JOYSTICK_HIDAPI by default on iOS

If you enable this, you'll need to link with CoreBluetooth.framework and add something like this to your Info.plist:
<key>NSBluetoothPeripheralUsageDescription</key>
<string>MyApp would like to remain connected to nearby bluetooth Game Controllers and Game Pads even when you're not using the app.</string>

src/hidapi/linux/hid.c

@@ -20,6 +20,9 @@
  code repository located at:
         http://github.com/signal11/hidapi .
 ********************************************************/
+#include "../../SDL_internal.h"
+
+#ifdef SDL_JOYSTICK_HIDAPI
 
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE /* needed for wcsdup() before glibc 2.10 */
@@ -891,3 +894,5 @@ HID_API_EXPORT const wchar_t * HID_API_CALL  hid_error(hid_device *dev)
 #ifdef NAMESPACE
 }
 #endif
+
+#endif /* SDL_JOYSTICK_HIDAPI */