So upstream went and added a mutex_enter_interruptible() which Linux calls mutex_lock_interruptible() and FreeBSD sx_xlock_sig(lock).
I was simply going to point it to lck_mtx_lock() and call it a day and ignoring the interruptible bit, but I am curious if there is a way to achieve something similar on XNU.
In this case, to be able to hit ^C in userland, get a signal, and have lck_mtx_lock() or variant, giveup and return error.