[Bug libstdc++/91906] std::timed_mutex::try_lock_until may not wait for timeout to expire when called with user-defined clock

[mac at mcrowe dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91906

--- Comment #1 from Mike Crowe <mac at mcrowe dot com> ---
Proposed fix for std::timed_mutex and std::shared_timed_mutex in series posted
for review at https://gcc.gnu.org/ml/gcc-patches/2019-09/msg01646.html .