D-Programming-Language/druntime — pull request #755 by tom-tan (2014-03-24 16:44:14+00:00)
Title: Mark some functions in core.sys.posix.unistd as safe and nothrow

Obviously they do not throw any exceptions.
Most functions which takes only integral types (or no arguments) do not cause undefined behaviors.
I leave `vfork` (it takes no arguments) as is because the manpage describes that it may cause undefined behaviors.