[Bug libstdc++/71684] Memory leak with std::mutex and std::lock_guard on freebsd

[Stromeko at nexgo dot de via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71684

--- Comment #14 from ASSI <Stromeko at nexgo dot de> ---
The same issue exists in shared_mutex via PTHREAD_RWLOCK_INITIALIZER (which
again is a struct on Cygwin).