[Bug c++/65255] std::thread does not work for cross compiling on ARM

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65255

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> ---
It's supported fine, but you need to compile your code that uses std::thread so
it is compatible with the libstdc++.so library you link to.

If libstdc++ is compiled to use atomic operations in shared_ptr then you need
to compile your code so it also uses atomics. If libstdc++ is compiled to use
mutexes in shared_ptr then you need to compile your code the same way.