patch 8.0.1215: newer gcc warns for implicit fallthrough

Problem:    Newer gcc warns for implicit fallthrough.
Solution:   Consistently use a FALLTHROUGH comment. (Christian Brabandt)
diff --git a/src/ex_getln.c b/src/ex_getln.c
index 6876a21..ba6a403 100644
--- a/src/ex_getln.c
+++ b/src/ex_getln.c
@@ -1563,9 +1563,8 @@
 			break;
 		    goto cmdline_not_changed;
 		}
-		/* FALLTHROUGH */
-
 #ifdef FEAT_CMDHIST
+		/* FALLTHROUGH */
 	case K_UP:
 	case K_DOWN:
 	case K_S_UP: