we can't really escape the fact that the very base-level Apple header…

… TargetConditionals.h defines both TARGET_OS_MAC and TARGET_OS_WIN32 (mutually exclusively as 0 or 1), so we need to treat both values as valid in our macros checks

* also WIN32 appears nowhere (_WIN32 is the default-defined macro of MSVC), so removed that from the macro checks
* perhaps instances of _WIN32 in our codebase should be migrated to TARGET_OS_WIN32 if that is now Tom's preferred macro to check?

dfx-library/dfxplugin-base.h

@@ -1,7 +1,7 @@
 /*------------------------------------------------------------------------
 Destroy FX Library is a collection of foundation code 
 for creating audio processing plug-ins. 
-Copyright (C) 2002-2020 Sophia Poirier
+Copyright (C) 2002-2020 Sophia Poirier and Tom Murphy 7
 
 This file is part of the Destroy FX Library (version 1.0).
 
@@ -144,18 +144,6 @@ To contact the author, use the contact form at http:https://destroyfx.org/
 #error TARGET_API_AUDIOSUITE should be defined to 1, if defined
 #endif
 
-#if defined(TARGET_OS_MAC) && TARGET_OS_MAC - 0 != 1
-#error TARGET_OS_MAC should be defined to 1, if defined
-#endif
-
-#if defined(WINDOWS) && WINDOWS - 0 != 1
-#error WINDOWS should be defined to 1, if defined
-#endif
-
-#if defined(WIN32) && WIN32 - 0 != 1
-#error WIN32 should be defined to 1, if defined
-#endif
-
 #if defined(DFX_SUPPORT_OLD_VST_SETTINGS) && DFX_SUPPORT_OLD_VST_SETTINGS - 0 != 1
 #error DFX_SUPPORT_OLD_VST_SETTINGS should be defined to 1, if defined
 #endif
@@ -183,6 +171,18 @@ To contact the author, use the contact form at http:https://destroyfx.org/
 #error TARGET_PLUGIN_HAS_GUI should be defined to 0 or 1
 #endif
 
+#if defined(TARGET_OS_MAC) && (0 - TARGET_OS_MAC - 1) == 1
+#error TARGET_OS_MAC should be defined to 0 or 1
+#endif
+
+#if defined(TARGET_OS_WIN32) && (0 - TARGET_OS_WIN32 - 1) == 1 
+#error TARGET_OS_WIN32 should be defined to 0 or 1
+#endif
+
+#if defined(WINDOWS) && (0 - WINDOWS - 1) == 1 
+#error WINDOWS should be defined to 0 or 1
+#endif
+
 namespace dfx
 {