[Bug c++/59256] qualified name in friend function declaration doesn't match previous declaration in inline namespace

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59256

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
It only affects --enable-symvers=gnu-versioned-namespace not the default
config, but it makes <regex> unusable. We can work around it if needed by
moving __regex_algo_impl out of the __detail namespace.