Fix class/struct mismatch C++ ABI [-Wmismatched-tags]

libs/evoral/evoral/Control.h

@@ -35,7 +35,7 @@
 
 namespace Evoral {
 
-class ParameterDescriptor;
+struct ParameterDescriptor;
 class Transport;
 class TypeMap;
 

libs/evoral/evoral/TypeMap.h

@@ -29,7 +29,7 @@
 namespace Evoral {
 
 class Parameter;
-class ParameterDescriptor;
+struct ParameterDescriptor;
 
 /** The applications passes one of these which provide the implementation
  * with required information about event types in an opaque, type neutral way

libs/surfaces/mackie/subview.h

@@ -25,7 +25,7 @@
 #include "ardour/types.h"
 
 namespace ARDOUR {
-	class ParameterDescriptor;
+	struct ParameterDescriptor;
 	class Plugin;
 	class PluginInsert;
 }

libs/widgets/widgets/pane.h

@@ -41,7 +41,7 @@ namespace ArdourWidgets {
 class LIBWIDGETS_API Pane : public Gtk::Container
 {
 private:
-	class Divider;
+	struct Divider;
 
 public:
 	struct Child