Switch to C++ versions of standard C headers

src/tests/base64.cc

@@ -37,9 +37,9 @@
    client and server.  It does not particularly test any code written for
    the Mosh project. */
 
-#include <stdint.h>
-#include <string.h>
-#include <stdlib.h>
+#include <cstdint>
+#include <cstring>
+#include <cstdlib>
 
 #include "src/crypto/base64.h"
 #include "base64_vector.h"