http://dlang.org/phobos/core_atomic.html
Document for core.atomic module is empty( or exposes no functions).
If you MAKE druntime with win32.mak, you get the right contents.
But with posix.mak, not. ( though I don't have that environment )
The cause is that the flag '-version=CoreDdoc' is dropped from DOCFMT macro(, maybe unexpectedly).
That is appended on May 20, and dropped on June 26.