std: Better handing of POLLHUP in ChildProcess (#8988)
std: Better handing of POLLHUP in ChildProcess (#8988)

* std: Better handing of POLLHUP in ChildProcess

Upon hitting the EOF condition there are two main differences between
how Linux and the *BSD-derived systems behave: the former sets POLLHUP
and POLLIN and, after reading any residual data, only POLLHUP remains
set. The latter signal the EOF condition by setting both flags thus
requiring some extra checks to determine if the stream is "done".

DragonFly workaround/hack for POLLHUP is no longer required.

Closes #8969
andrewrk/zig,zig-lang/zig,andrewrk/zig,zig-lang/zig,zig-lang/zig