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/window.c b/src/window.c
index 96e32d8..ad084a4 100644
--- a/src/window.c
+++ b/src/window.c
@@ -433,8 +433,8 @@
 		    g_do_tagpreview = Prenum;
 		else
 		    g_do_tagpreview = p_pvh;
-		/*FALLTHROUGH*/
 #endif
+		/* FALLTHROUGH */
     case ']':
     case Ctrl_RSB:
 		CHECK_CMDWIN
@@ -557,8 +557,8 @@
 			    g_do_tagpreview = Prenum;
 			else
 			    g_do_tagpreview = p_pvh;
-			/*FALLTHROUGH*/
 #endif
+			/* FALLTHROUGH */
 		    case ']':
 		    case Ctrl_RSB:
 			/* keep Visual mode, can select words to use as a tag */