Fix mingw VST3 build (atomic add)

Signed-off-by: falkTX <falktx@falktx.com>

modules/juce_audio_processors/format_types/VST3_SDK/pluginterfaces/base/funknown.cpp

@@ -67,11 +67,11 @@ namespace FUnknownPrivate {
 //------------------------------------------------------------------------
 int32 PLUGIN_API atomicAdd (int32& var, int32 d)
 {
-#if SMTG_OS_WINDOWS
+#if SMTG_OS_WINDOWS && !defined(__MINGW32__)
 	return InterlockedExchangeAdd (&var, d) + d;
 #elif SMTG_OS_MACOS
 	return OSAtomicAdd32Barrier (d, (int32_t*)&var);
-#elif SMTG_OS_LINUX
+#elif SMTG_OS_LINUX || defined(__MINGW32__)
 	__gnu_cxx::__atomic_add (&var, d);
 	return var;
 #else