Ignore the return value of strerror_r().

Ignore the return value of strerror_r().

If it fails, it either means 1) the buffer was too short, but it
provided a truncated message, and we're not going to allocate a bigger
buffer to make it work, or 2) the errno doesn't have a string
corresponding to it, but it provided a message of some sort for the
error, even if it's just something like "Unknown error", and we're not
going to construct our own message.