atomic_cas_ptr() is for compare-and-swap pointer addresses.
So when building 64 bit:
1. `ptr` is used casted to a pointer value (4-byte into 8-byte).
2. atomic_cas_ptr reads 8-byte at `ptr` and returns
In the case of `uv_async_send`, if handle->pending is 0, cmpxchgi()
actually returns the value of the 4-bytes past handle->pending,
causing uv__async_send to never be called.
The modified test-async-null-cb.c hangs at uv_run in this case.
PR-URL: https://github.com/libuv/libuv/pull/1361
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
d0a27baa7d