Avoid a warning in the VST3 headers when building with Xcode 10

modules/juce_audio_processors/format_types/juce_VST3Headers.h

@@ -47,6 +47,7 @@
  #pragma clang diagnostic ignored "-Wdeprecated-declarations"
  #pragma clang diagnostic ignored "-Wextra-semi"
  #pragma clang diagnostic ignored "-Wmissing-braces"
+ #pragma clang diagnostic ignored "-Wpragma-pack"
  #if __has_warning("-Wcomma")
   #pragma clang diagnostic ignored "-Wcomma"
  #endif