[Bug c++/70476] C++11: Function name declared in unnamed namespace extern "C" gets exernal linkage

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70476

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
And this means the functions I thought were local to src/c++11/thread.cc are
not ... drat.