Fix missing XFixes build

Make sure we can actually build without XFixes libraries.

unix/x0vncserver/XDesktop.cxx

@@ -947,6 +947,7 @@ void XDesktop::queryRejected()
   queryConnectSock = 0;
 }
 
+#ifdef HAVE_XFIXES
 bool XDesktop::setCursor()
 {
   XFixesCursorImage *cim;
@@ -994,3 +995,4 @@ bool XDesktop::setCursor()
   XFree(cim);
   return true;
 }
+#endif

unix/x0vncserver/XDesktop.h

@@ -105,7 +105,9 @@ protected:
   void deleteAddedKeysyms(Display* dpy);
   KeyCode keysymToKeycode(Display* dpy, KeySym keysym);
 #endif
+#ifdef HAVE_XFIXES
   bool setCursor();
+#endif
   rfb::ScreenSet computeScreenLayout();
 };