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/regexp_nfa.c b/src/regexp_nfa.c
index 40d6605..86061a3 100644
--- a/src/regexp_nfa.c
+++ b/src/regexp_nfa.c
@@ -1320,7 +1320,7 @@
 		goto collection;
 
 	/* "\_x" is character class plus newline */
-	/*FALLTHROUGH*/
+	/* FALLTHROUGH */
 
 	/*
 	 * Character classes.
@@ -4698,6 +4698,7 @@
 		subs = addstate(l, state->out, subs, pim, off_arg);
 		break;
 	    }
+	    /* FALLTHROUGH */
 	case NFA_MCLOSE1:
 	case NFA_MCLOSE2:
 	case NFA_MCLOSE3: