X11TK: Use SDL_roundf instead of normal roundf

src/video/x11/SDL_x11toolkit.c

@@ -412,7 +412,7 @@ static void X11Toolkit_SettingsNotify(const char *name, XSettingsAction action,
         /* set scale vars */
         window->scale = X11Toolkit_GetUIScale(window->xsettings, window->display);
         window->iscale = (int)SDL_ceilf(window->scale);
-        if (roundf(window->scale) == window->scale) {
+        if (SDL_roundf(window->scale) == window->scale) {
             window->scale = 0;
         }
         
@@ -618,7 +618,7 @@ SDL_ToolkitWindowX11 *X11Toolkit_CreateWindowStruct(SDL_Window *parent, SDL_Tool
     window->xsettings_first_time = false;
     window->scale = X11Toolkit_GetUIScale(window->xsettings, window->display);
     window->iscale = (int)SDL_ceilf(window->scale);
-    if (roundf(window->scale) == window->scale) {
+    if (SDL_roundf(window->scale) == window->scale) {
         window->scale = 0;
     }