Fix build on Linux and Mac

src/Project.h

@@ -31,6 +31,7 @@
 #include "xml/XMLTagHandler.h"
 #include "toolbars/SelectionBarListener.h"
 #include "toolbars/SpectralSelectionBarListener.h"
+#include "widgets/Meter.h"
 
 #include <wx/defs.h>
 #include <wx/event.h>

src/toolbars/MeterToolBar.h

@@ -15,6 +15,7 @@
 #define __AUDACITY_METER_TOOLBAR__
 
 #include "ToolBar.h"
+#include "../Project.h"
 
 class wxDC;
 class wxGridBagSizer;