https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109936
--- Comment #19 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Andreas Schwab from comment #10)
> It is a valid preprocessing token ("non-whitespace character that cannot be
> one of the above").
Ah right, yes. It's a preprocessing token, but is never converted to a token,
so doesn't need to be a keyword, identifier etc.
