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/spell.c b/src/spell.c
index eb1b9fb..cdcf822 100644
--- a/src/spell.c
+++ b/src/spell.c
@@ -5019,7 +5019,7 @@
 	    }
 	    PROF_STORE(sp->ts_state)
 	    sp->ts_state = STATE_PLAIN;
-	    /*FALLTHROUGH*/
+	    /* FALLTHROUGH */
 
 	case STATE_PLAIN:
 	    /*
@@ -5243,7 +5243,7 @@
 		}
 		break;
 	    }
-	    /*FALLTHROUGH*/
+	    /* FALLTHROUGH */
 
 	case STATE_INS_PREP:
 	    if (sp->ts_flags & TSF_DIDDEL)
@@ -5277,7 +5277,7 @@
 	    }
 	    break;
 
-	    /*FALLTHROUGH*/
+	    /* FALLTHROUGH */
 
 	case STATE_INS:
 	    /* Insert one byte.  Repeat this for each possible byte at this
@@ -5464,7 +5464,7 @@
 		*p = p[1];
 		p[1] = c;
 	    }
-	    /*FALLTHROUGH*/
+	    /* FALLTHROUGH */
 
 	case STATE_SWAP3:
 	    /* Swap two bytes, skipping one: "123" -> "321".  We change
@@ -5703,7 +5703,7 @@
 		p[1] = p[2];
 		p[2] = c;
 	    }
-	    /*FALLTHROUGH*/
+	    /* FALLTHROUGH */
 
 	case STATE_REP_INI:
 	    /* Check if matching with REP items from the .aff file would work.
@@ -5736,7 +5736,7 @@
 
 	    PROF_STORE(sp->ts_state)
 	    sp->ts_state = STATE_REP;
-	    /*FALLTHROUGH*/
+	    /* FALLTHROUGH */
 
 	case STATE_REP:
 	    /* Try matching with REP items from the .aff file.  For each match