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/ios/hid.m

@@ -3,6 +3,9 @@
 // Purpose: HID device abstraction temporary stub
 //
 //=============================================================================
+#include "../../SDL_internal.h"
+
+#ifdef SDL_JOYSTICK_HIDAPI
 
 #include <CoreBluetooth/CoreBluetooth.h>
 #include <QuartzCore/QuartzCore.h>
@@ -907,3 +910,5 @@ int HID_API_EXPORT hid_read_timeout(hid_device *dev, unsigned char *data, size_t
 #endif
 	return result;
 }
+
+#endif /* SDL_JOYSTICK_HIDAPI */