[Bug libstdc++/89740] reading from cin & writing to cout sync_with_stdio(false) has race conditions

[ahu at ds9a dot nl]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89740

--- Comment #2 from bert hubert <ahu at ds9a dot nl> ---
Created attachment 45982
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=45982&action=edit
reproduction that actually shows the bug

This is the version of the reproduction that exhibits the problem. The other
version had the "fix" included, cin.tie(nullptr), and thus did not have the
problem.