We don't define PRIu8 or PRIx8 if the C environment doesn't; don't use it.

The right format to use to print 8-bit quantities isn't
implementation-dependent, so no need to use the PRIu8 and PRIx8 macros.

There's also no need for an empty string after PRIu64.  Separate it with
space from the strings with which it's being concatenated, however; we
do that elsewhere.