Should we be asserting in atomic/barrier/latch/semaphore`

[brycelelbach]

The only places in libc++ that seem to assert are places where we have added asserts - the CUDA backend for atomic, upstream barrier, latch, and semaphore. Should we really be using assert in Standard Library code?

[miscco]

In NVIDIA/libcudacxx#372 I am reworking this to use _LIBCUDACXX_ASSERT which should be opt in and easier to disable