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/bionic/syslog.cpp b/libc/bionic/syslog.cpp
index d8b8b19..8e3f34f 100644
--- a/libc/bionic/syslog.cpp
+++ b/libc/bionic/syslog.cpp
@@ -16,6 +16,7 @@
 
 #include <errno.h>
 #include <stdlib.h>
+#include <string.h>
 #include <syslog.h>
 
 #include "private/libc_logging.h"