Added missing X11 symbol.

src/video/x11/SDL_x11sym.h

@@ -110,6 +110,7 @@ SDL_X11_SYM(int,XUndefineCursor,(Display* a,Window b),(a,b),return)
 SDL_X11_SYM(int,XUngrabKeyboard,(Display* a,Time b),(a,b),return)
 SDL_X11_SYM(int,XUngrabPointer,(Display* a,Time b),(a,b),return)
 SDL_X11_SYM(int,XUngrabServer,(Display* a),(a),return)
+SDL_X11_SYM(int,XUninstallColormap,(Display* a,Colormap b),(a,b),return)
 SDL_X11_SYM(int,XUnmapWindow,(Display* a,Window b),(a,b),return)
 SDL_X11_SYM(int,XWarpPointer,(Display* a,Window b,Window c,int d,int e,unsigned int f,unsigned int g,int h,int i),(a,b,c,d,e,f,g,h,i),return)
 SDL_X11_SYM(VisualID,XVisualIDFromVisual,(Visual* a),(a),return)