cc: nit: silence comment warnings

R=golang-dev, r, r
CC=golang-dev
https://golang.org/cl/4648043

src/cmd/6c/cgen.c

@@ -1544,7 +1544,7 @@ sugen(Node *n, Node *nn, int32 w)
 			nod0.addable = 0;
 			nod0.right = l;
 
-			/* prtree(&nod0, "hand craft"); /* */
+			// prtree(&nod0, "hand craft");
 			cgen(&nod0, Z);
 		}
 		break;

src/cmd/8c/cgen.c

@@ -1581,7 +1581,7 @@ sugen(Node *n, Node *nn, int32 w)
 			nod0.addable = 0;
 			nod0.right = l;
 
-			/* prtree(&nod0, "hand craft"); /* */
+			// prtree(&nod0, "hand craft");
 			cgen(&nod0, Z);
 		}
 		break;

src/cmd/cc/dcl.c

@@ -1378,7 +1378,6 @@ tmerge(Type *t1, Sym *s)
 	Type *ta, *tb, *t2;
 
 	t2 = s->type;
-/*print("merge	%T; %T\n", t1, t2);/**/
 	for(;;) {
 		if(t1 == T || t2 == T || t1 == t2)
 			break;