message: random: use arc4random on OpenBSD
  Following best practices on OpenBSD. The getentropy(2) man page states:
  "getentropy() is not intended for regular code;
  please use the arc4random(3) family of functions instead."
diff: @@ -305,16 +305,14 @@ void GetOSRand(unsigned char *ent32)
  RandFailure();
  }
  }
  -#elif defined(HAVE_GETENTROPY) && defined(__OpenBSD__)
  - /* On OpenBSD this can return up to 256 bytes of entropy, will return an
  - * error if more are requested.
  - * The call cannot return less than the requested number of bytes.
  - getentropy is explicitly limited to openbsd here, as a similar (but not
  - the same) function may exist on other platforms via glibc.
  +#elif defined(__OpenBSD__)
  + /* OpenBSD. From the arc4random(3) man page:
  + "Use of these functions is encouraged for almost all random number
  + consumption because the other interfaces are deficient in either
  + quality, portability, standardization, or availability."
  + The function call is always successful.
  */
  - if (getentropy(ent32, NUM_OS_RANDOM_BYTES) != 0) {
  - RandFailure();
  - }
  + arc4random_buf(ent32, NUM_OS_RANDOM_BYTES);
  // Silence a compiler warning about unused function.
  (void)GetDevURandom;
  #elif defined(HAVE_GETENTROPY_RAND) && defined(MAC_OSX)
  