Add missing #includes

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

src/crypto/crypto.cc

@@ -18,6 +18,8 @@
 
 #include <string.h>
 #include <stdio.h>
+#include <errno.h>
+#include <stdlib.h>
 
 #include "crypto.h"
 #include "base64.h"