patch 8.1.0795: cannot build without popup menu

Problem:    Cannot build without popup menu.
Solution:   Add #ifdef
diff --git a/src/ex_getln.c b/src/ex_getln.c
index 9400b20..f7dfc32 100644
--- a/src/ex_getln.c
+++ b/src/ex_getln.c
@@ -7268,9 +7268,11 @@
     /* Don't execute autocommands while creating the window. */
     block_autocmds();
 
+#if defined(FEAT_INS_EXPAND)
     // When using completion in Insert mode with <C-R>=<C-F> one can open the
     // command line window, but we don't want the popup menu then.
     pum_undisplay();
+#endif
 
     /* don't use a new tab page */
     cmdmod.tab = 0;