8g,8l: fix "set but not used" gcc error

$ gcc --version
gcc (GCC) 4.6.0 20110415 (prerelease)

R=golang-dev, rsc1, rsc
CC=golang-dev
https://golang.org/cl/4442080

src/cmd/8g/ggen.c

@@ -625,12 +625,8 @@ void
 cgen_div(int op, Node *nl, Node *nr, Node *res)
 {
 	Node ax, dx, oldax, olddx;
-	int rax, rdx;
 	Type *t;
 
-	rax = reg[D_AX];
-	rdx = reg[D_DX];
-
 	if(is64(nl->type))
 		fatal("cgen_div %T", nl->type);
 

src/cmd/8l/obj.c

@@ -431,7 +431,7 @@ ldobj1(Biobuf *f, char *pkg, int64 len, char *pn)
 	int32 ipc;
 	Prog *p;
 	int v, o, r, skip;
-	Sym *h[NSYM], *s, *di;
+	Sym *h[NSYM], *s;
 	uint32 sig;
 	int ntext;
 	int32 eof;
@@ -442,7 +442,6 @@ ldobj1(Biobuf *f, char *pkg, int64 len, char *pn)
 	lastp = nil;
 	ntext = 0;
 	eof = Boffset(f) + len;
-	di = S;
 	src[0] = 0;