[Bug libstdc++/64735] std::future broken on armel

[suokkos at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64735

--- Comment #9 from Pauli <suokkos at gmail dot com> ---
atomicity.h uses exactly same builtins if _GLIBCXX_ATOMIC_BUILTINS is set 1.
Difference include check for __gthread_active_p check and annotations for race
detector. Annotations are empty macros in default build. Same code is uses for
all other atomic operations in libstdc++.

I'm finally having an working armv5te build from gcc-6-branch. I'm currently
waiting the second unit test run to complete. If there is no unexpected
failures from futures or exceptions I fill submit the complete patch later
today.