Fix additional warnings when Carla is missing (#7722)

Fix additional warnings when Carla is missing
Adds new env var LMMS_EXCLUDE_LADSPA

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Co-authored-by: Dalton Messmer <messmer.dalton@gmail.com>

include/PluginFactory.h

@@ -61,6 +61,7 @@ public:
 	~PluginFactory() = default;
 
 	static void setupSearchPaths();
+	static QList<QRegularExpression> getExcludePatterns(const char* envVar);
 
 	/// Returns the singleton instance of PluginFactory. You won't need to call
 	/// this directly, use pluginFactory instead.