Add DWM_WINDOW_CORNER_PREFERENCE enum for window corner preferences

core/sys/windows/dwmapi.odin

@@ -38,6 +38,13 @@ DWMNCRENDERINGPOLICY :: enum {
 	DWMNCRP_LAST,
 }
 
+DWM_WINDOW_CORNER_PREFERENCE :: enum c_int{
+   DEFAULT,
+   DONOTROUND,
+   ROUND,
+   ROUNDSMALL,
+}
+
 @(default_calling_convention="system")
 foreign dwmapi {
 	DwmFlush :: proc() -> HRESULT ---