[Bug libstdc++/67015] "^[a-z0-9][a-z0-9-]*$", std::regex::extended is miscompiled

[rleigh at debian dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67015

--- Comment #2 from Roger Leigh <rleigh at debian dot org> ---
Note regex2.cc fails with 4.9.2 but not with 4.9.3 or 5.1, so this appear to
have been fixed.