In many cases the unistd.h includes weren't actually needed.
Don't build tests that need it on windows with MSVC
(multifdsink, multisocketsink, pipelines/tcp).
Preparation for making tests work on Windows with MSVC.
Previously, the source posted a TAG message before buffers would
even be pushed towards the sink, so we'd get the TAG message before
any ASYNC_DONE message. Now the tags get sent downstream to the sink
to get posted there, and the tag event will get queued and handled
later after preroll has finished, so now we get the ASYNC_DONE
message before the TAG message.
