Implement Fl_Wayland_Screen_Driver::base_scale(int numscreen)

src/drivers/Wayland/Fl_Wayland_Screen_Driver.H

@@ -171,6 +171,7 @@ public:
   void enable_im() FL_OVERRIDE;
   void disable_im() FL_OVERRIDE;
   bool screen_boundaries_known() FL_OVERRIDE { return false; }
+  float base_scale(int numscreen) FL_OVERRIDE;
 
   // overridden functions from parent class Fl_Unix_Screen_Driver
   int poll_or_select_with_delay(double time_to_wait) FL_OVERRIDE;

src/drivers/Wayland/Fl_Wayland_Screen_Driver.cxx

@@ -1877,6 +1877,11 @@ int Fl_Wayland_Screen_Driver::get_key(int k) {
 }
 
 
+float Fl_Wayland_Screen_Driver::base_scale(int numscreen) {
+  return 1.f;
+}
+
+
 struct wl_display *fl_wl_display() {
   return Fl_Wayland_Screen_Driver::wl_display;
 }