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_core/threads/juce_SpinLock.h

@@ -0,0 +1,85 @@
+/*
+  ==============================================================================
+
+   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.
+
+   The code included in this file is provided under the terms of the ISC license
+   http://www.isc.org/downloads/software-support-policy/isc-license. Permission
+   To use, copy, modify, and/or distribute this software for any purpose with or
+   without fee is hereby granted provided that the above copyright notice and
+   this permission notice appear in all copies.
+
+   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
+{
+
+//==============================================================================
+/**
+    A simple spin-lock class that can be used as a simple, low-overhead mutex for
+    uncontended situations.
+
+    Note that unlike a CriticalSection, this type of lock is not re-entrant, and may
+    be less efficient when used in a highly contended situation, but it's very small and
+    requires almost no initialisation.
+    It's most appropriate for simple situations where you're only going to hold the
+    lock for a very brief time.
+
+    @see CriticalSection
+
+    @tags{Core}
+*/
+class JUCE_API  SpinLock
+{
+public:
+    inline SpinLock() noexcept {}
+    inline ~SpinLock() noexcept {}
+
+    /** Acquires the lock.
+        This will block until the lock has been successfully acquired by this thread.
+        Note that a SpinLock is NOT re-entrant, and is not smart enough to know whether the
+        caller thread already has the lock - so if a thread tries to acquire a lock that it
+        already holds, this method will never return!
+
+        It's strongly recommended that you never call this method directly - instead use the
+        ScopedLockType class to manage the locking using an RAII pattern instead.
+    */
+    void enter() const noexcept;
+
+    /** Attempts to acquire the lock, returning true if this was successful. */
+    inline bool tryEnter() const noexcept
+    {
+        return lock.compareAndSetBool (1, 0);
+    }
+
+    /** Releases the lock. */
+    inline void exit() const noexcept
+    {
+        jassert (lock.get() == 1); // Agh! Releasing a lock that isn't currently held!
+        lock = 0;
+    }
+
+    //==============================================================================
+    /** Provides the type of scoped lock to use for locking a SpinLock. */
+    typedef GenericScopedLock <SpinLock>       ScopedLockType;
+
+    /** Provides the type of scoped unlocker to use with a SpinLock. */
+    typedef GenericScopedUnlock <SpinLock>     ScopedUnlockType;
+
+private:
+    //==============================================================================
+    mutable Atomic<int> lock;
+
+    JUCE_DECLARE_NON_COPYABLE (SpinLock)
+};
+
+} // namespace juce