Merge branch '12.6.x' into '12.6.x'

arma_ignore Xst backport

See merge request conradsnicta/armadillo-code!144

include/armadillo_bits/sp_auxlib_meat.hpp

@@ -2062,6 +2062,7 @@ sp_auxlib::run_aupd_plain
     arma_ignore(n_eigvals);
     arma_ignore(which);
     arma_ignore(X);
+    arma_ignore(Xst);
     arma_ignore(sym);
     arma_ignore(n);
     arma_ignore(tol);