patch 8.1.1971: manually enabling features causes build errors

Problem:    Manually enabling features causes build errors. (John Marriott)
Solution:   Adjust #ifdefs.
diff --git a/src/popupmnu.c b/src/popupmnu.c
index c25cff2..da70c5f 100644
--- a/src/popupmnu.c
+++ b/src/popupmnu.c
@@ -760,8 +760,9 @@
 # else
 #  define use_popup 0
 # endif
+# ifdef FEAT_TEXT_PROP
 	    has_info = TRUE;
-
+# endif
 	    // Open a preview window.  3 lines by default.  Prefer
 	    // 'previewheight' if set and smaller.
 	    g_do_tagpreview = 3;