VST3 Client: Fix missing-prototype warning

modules/juce_audio_plugin_client/utility/juce_PluginUtilities.cpp

@@ -47,6 +47,7 @@ namespace juce
  #define VST3_REPLACEMENT_AVAILABLE 1
 
  // NB: Nasty old-fashioned code in here because it's copied from the Steinberg example code.
+ void getUUIDForVST2ID (bool forControllerUID, uint8 uuid[16]);
  void getUUIDForVST2ID (bool forControllerUID, uint8 uuid[16])
  {
      #if JUCE_MSVC