build: fix more unused parameters

R=ken2
CC=golang-dev
https://golang.org/cl/4971042

src/cmd/5g/gsubr.c

@@ -86,6 +86,8 @@ gbranch(int as, Type *t)
 {
 	Prog *p;
 
+	USED(t);
+
 	p = prog(as);
 	p->to.type = D_BRANCH;
 	p->to.branch = P;

src/cmd/8g/gobj.c

@@ -549,6 +549,8 @@ genembedtramp(Type *rcvr, Type *method, Sym *newnam, int iface)
 	Prog *p;
 	Type *f;
 
+	USED(iface);
+
 	e = method->sym;
 	for(d=0; d<nelem(dotlist); d++) {
 		c = adddot1(e, rcvr, d, nil, 0);

src/cmd/8g/gsubr.c

@@ -84,6 +84,7 @@ gbranch(int as, Type *t)
 {
 	Prog *p;
 
+	USED(t);
 	p = prog(as);
 	p->to.type = D_BRANCH;
 	p->to.branch = P;
@@ -1957,5 +1958,9 @@ sudoclean(void)
 int
 sudoaddable(int as, Node *n, Addr *a)
 {
+	USED(as);
+	USED(n);
+	USED(a);
+
 	return 0;
 }