patch 8.0.1463: test fails without 'autochdir' option

Problem:    Test fails without 'autochdir' option.
Solution:   Skip test if 'autochdir' is not supported.
diff --git a/src/testdir/test_autocmd.vim b/src/testdir/test_autocmd.vim
index c504f70..065ac4e 100644
--- a/src/testdir/test_autocmd.vim
+++ b/src/testdir/test_autocmd.vim
@@ -1232,6 +1232,9 @@
 endfunc
 
 function Test_dirchanged_auto()
+  if !exists('+autochdir')
+    return
+  endif
   call s:Before_test_dirchanged()
   call test_autochdir()
   autocmd test_dirchanged DirChanged auto call add(s:li, "auto:")