https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80955
--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> --- Is there a way to check if it's a pre-defined macro? Or just change the condition to allow starting with two underscores, but not allow starting with one (since user-defined UDLs must start with a single underscore, and must not start with two).
