[c++-pthreads] thread-safety definition

[Ted Baker]

> Heck, let's mandate to have async-cancel-safe strlen()-and-alike
> stuff "in-addition-to OR instead-of" async-cancel-unsafe stuff 
> and simply use C++ function overloading to pick the right stuff 
> (async_cancel_safe inside async_cancel{}), okay?

A joke?  (With nested calls and separate compilation you obviously
cannot tell what call is "inside" an async_cancel{}.)

--Ted