The old __regex_word aliased the mask for xdigit, causing stray
The diff may look surprising, as if the previous faulty value had
been set specifically for Windows - but this is due to a restructuring
in 411c630bae0e0d50697651797709987e2cfea92d. Prior to that, there
were OS specific settings for some OSes, and one fallback used for
the rest (which turns out to not work for Windows).