Fix three clang complaints about the DNS code.

These are all already fixed upstream in the same way.

Change-Id: I2881b6d0fbd0237fffc0f00563bc14750dcce0d9
diff --git a/libc/dns/resolv/res_state.c b/libc/dns/resolv/res_state.c
index 01f68e9..57791d1 100644
--- a/libc/dns/resolv/res_state.c
+++ b/libc/dns/resolv/res_state.c
@@ -211,10 +211,9 @@
 }
 
 void
-__res_put_state(res_state res)
+__res_put_state(res_state res __unused)
 {
     /* nothing to do */
-    res=res;
 }
 
 res_static