fix macOS build (following Projucer changes made in Windows, which removed /Applications/JUCE/modules from its headers). move JUCE headers under source control, so that Windows and macOS can both build against same version of JUCE. remove AUv3 target (I think it's an iOS thing, so it will never work with this macOS fluidsynth dylib).

modules/juce_audio_plugin_client/AAX/juce_AAX_Modifier_Injector.h

@@ -0,0 +1,47 @@
+/*
+  ==============================================================================
+
+   This file is part of the JUCE library.
+   Copyright (c) 2017 - ROLI Ltd.
+
+   JUCE is an open source library subject to commercial or open-source
+   licensing.
+
+   By using JUCE, you agree to the terms of both the JUCE 5 End-User License
+   Agreement and JUCE 5 Privacy Policy (both updated and effective as of the
+   27th April 2017).
+
+   End User License Agreement: www.juce.com/juce-5-licence
+   Privacy Policy: www.juce.com/juce-5-privacy-policy
+
+   Or: You may also use this code under the terms of the GPL v3 (see
+   www.gnu.org/licenses).
+
+   JUCE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL WARRANTIES, WHETHER
+   EXPRESSED OR IMPLIED, INCLUDING MERCHANTABILITY AND FITNESS FOR PURPOSE, ARE
+   DISCLAIMED.
+
+  ==============================================================================
+*/
+
+namespace juce
+{
+
+#ifndef DOXYGEN
+
+struct ModifierKeyProvider
+{
+    virtual ~ModifierKeyProvider() {}
+    virtual int getWin32Modifiers() const = 0;
+};
+
+struct ModifierKeyReceiver
+{
+    virtual ~ModifierKeyReceiver() {}
+    virtual void setModifierKeyProvider (ModifierKeyProvider*) = 0;
+    virtual void removeModifierKeyProvider() = 0;
+};
+
+#endif
+
+} // namespace juce