[Bug c++/63497] std::regex can't handle [^class] correctly and cause runtime crash

[timshen at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63497

--- Comment #4 from Tim Shen <timshen at gcc dot gnu.org> ---
Hi Yue Wang, I'm sorry if my last reply looks scary. I should have put it in
libstdc++ list. I didn't mean to reply you with all implementation details.

Anyway, the cause is clear, and it will be fixed in trunk (and I believe that
it can be backported to 4.9 branch).

Thanks for reporting :)