The gthreads portability layer is missing a function for destroying a __ghtread_recursive_mutex object.
For pthreads-based models the recursive mutex type is the same as the normal mutex type so __gthread_mutex_destroy handles both, but they're distinct types for (at least) gthr-win32.h, so we can't properly cleanup recursive mutexes in libstdc++ Any objections if I prepare a patch to add __gthread_recursive_mutex_destroy to each gthr header?
