5c: attempt to fix build by silencing warnings about unused variables.

The story is more complicated; this is just a bandaid.

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/4755047

src/cmd/5c/reg.c

@@ -66,6 +66,11 @@ rcmp(const void *a1, const void *a2)
 void
 regopt(Prog *p)
 {
+	// TODO(kaib): optimizer disabled because it smashes R8 when running out of registers
+	// the disable is unconventionally here because the call is in common code shared by 5c/6c/8c
+	return;
+
+#ifdef	NOTDEF
 	Reg *r, *r1, *r2;
 	Prog *p1;
 	int i, z;
@@ -79,11 +84,6 @@ regopt(Prog *p)
 		Reg*	p;
 	} log5[6], *lp;
 
-	// TODO(kaib): optimizer disabled because it smashes R8 when running out of registers
-	// the disable is unconventionally here because the call is in common code shared by 5c/6c/8c
-	return;
-
-#ifdef	NOTDEF
 	firstr = R;
 	lastr = R;
 	nvar = 0;