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_box2d/box2d/Common/b2Settings.cpp

@@ -0,0 +1,41 @@
+/*
+* Copyright (c) 2006-2009 Erin Catto http://www.box2d.org
+*
+* This software is provided 'as-is', without any express or implied
+* warranty.  In no event will the authors be held liable for any damages
+* arising from the use of this software.
+* Permission is granted to anyone to use this software for any purpose,
+* including commercial applications, and to alter it and redistribute it
+* freely, subject to the following restrictions:
+* 1. The origin of this software must not be misrepresented; you must not
+* claim that you wrote the original software. If you use this software
+* in a product, an acknowledgment in the product documentation would be
+* appreciated but is not required.
+* 2. Altered source versions must be plainly marked as such, and must not be
+* misrepresented as being the original software.
+* 3. This notice may not be removed or altered from any source distribution.
+*/
+
+#include "b2Settings.h"
+
+b2Version b2_version = {2, 2, 1};
+
+// Memory allocators. Modify these to use your own allocator.
+void* b2Alloc(int32 size)
+{
+	return malloc(size);
+}
+
+void b2Free(void* mem)
+{
+	free(mem);
+}
+
+// You can modify this to use your logging facility.
+void b2Log(const char* string, ...)
+{
+	va_list args;
+	va_start(args, string);
+	vprintf(string, args);
+	va_end(args);
+}