api: Include <string.h> to avoid implicit function declarations

Author: fweimer-rh

api/libsphinxclient/test.c

@@ -16,6 +16,7 @@
 #include <stdarg.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 
 #if _WIN32
 #include <winsock2.h>