[Bug libstdc++/85098] undefined reference to std::regex::extended

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85098

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Reduced:

#include <regex>

void f(const std::regex_constants::syntax_option_type&) { }

int main() {
  f(std::regex::extended);
}