xpp: Update submodule (#2125)

* xpp: Update submodule

* aur: Force system python in polybar-git

This should resolve problems on systems with conda or pyenv enabled that
would otherwise not pick up xcbgen properly

contrib/polybar-git.aur/PKGBUILD

@@ -31,7 +31,8 @@ prepare() {
 
 build() {
   cd "${_pkgname}/build" || exit 1
-  cmake -DCMAKE_INSTALL_PREFIX=/usr ..
+  # Force cmake to use system python (to detect xcbgen)
+  cmake -DCMAKE_INSTALL_PREFIX=/usr -DPYTHON_EXECUTABLE=/usr/bin/python3 ..
   cmake --build .
 }