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

[christian.prochaska--- via Gcc-bugs]

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

--- Comment #7 from Christian Prochaska <christian.procha...@genode-labs.com> 
---
Bug 57440 solved the problem for mingw32 by defining
_GTHREAD_USE_MUTEX_INIT_FUNC in os_defines.h.