[Bug libstdc++/67361] New: std::regex_error::what() should say something about the error_code

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67361

            Bug ID: 67361
           Summary: std::regex_error::what() should say something about
                    the error_code
           Product: gcc
           Version: 4.9.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
  Target Milestone: ---

This would be more helpful if it included a string representation of the
error_code such as regex_constants::error_paren:

terminate called after throwing an instance of 'std::regex_error'
  what():  regex_error