libc: Add support for itoa and string reverse functions.

Change-Id: I483936db2e918922e8b14cfe18008a4746632de1
diff --git a/include/string.h b/include/string.h
index 3dccd92..661e746 100644
--- a/include/string.h
+++ b/include/string.h
@@ -54,6 +54,7 @@
 int         strcoll(const char *s1, const char *s2) __PURE;
 size_t      strxfrm(char *dest, const char *src, size_t n) __PURE;
 char       *strdup(const char *str) __MALLOC;
+void        strrev(unsigned char *str) __PURE;
 
 #ifdef __cplusplus
 } /* extern "C" */