Move extern in a2c80da to appropriate header file

distrho/DistrhoUI.hpp

@@ -54,6 +54,10 @@ END_NAMESPACE_DGL
 
 START_NAMESPACE_DISTRHO
 
+#ifdef DISTRHO_OS_MAC
+float getMacMainScreenBackingScaleFactor();
+#endif
+
 /* ------------------------------------------------------------------------------------------------------------
  * DPF UI */
 

distrho/src/DistrhoUI.cpp

@@ -184,10 +184,6 @@ void UI::uiFileBrowserSelected(const char*)
 /* ------------------------------------------------------------------------------------------------------------
  * UI Resize Handling, internal */
 
-# if DISTRHO_OS_MAC
-extern float getMacMainScreenBackingScaleFactor();
-# endif // DISTRHO_OS_MAC
-
 void UI::onResize(const ResizeEvent& ev)
 {
     UIWidget::onResize(ev);