empty switches -- bug128

R=r
OCL=20520
CL=20522

src/cmd/6g/gen.c

@@ -536,6 +536,8 @@ swgen(Node *n)
 	c1 = listfirst(&save1, &n->nbody);
 	while(c1 != N) {
 		setlineno(c1);
+		if(c1->op == OEMPTY)
+			break;
 		if(c1->op != OCASE) {
 			if(s0 == C && dflt == P)
 				yyerror("unreachable statements in a switch");

src/cmd/gc/walk.c

@@ -277,9 +277,7 @@ loop:
 		if(top != Etop)
 			goto nottop;
 
-		if(!casebody(n->nbody))
-			yyerror("switch statement must have case labels");
-
+		casebody(n->nbody);
 		if(n->ntest == N)
 			n->ntest = booltrue;
 		walkstate(n->ninit);