Clean up <stdlib.h> slightly.

Interestingly, this mostly involves cleaning up our implementation of
various <string.h> functions.

Change-Id: Ifaef49b5cb997134f7bc0cc31bdac844bdb9e089
diff --git a/libc/dns/resolv/res_state.c b/libc/dns/resolv/res_state.c
index 75bff97..7533d19 100644
--- a/libc/dns/resolv/res_state.c
+++ b/libc/dns/resolv/res_state.c
@@ -34,6 +34,7 @@
 #include "resolv_cache.h"
 #include <pthread.h>
 #include <stdlib.h>
+#include <string.h>
 
 #define _REALLY_INCLUDE_SYS__SYSTEM_PROPERTIES_H_
 #include <sys/_system_properties.h>