If you want to simulate building with POSIX timer support disabled,
you can do the following:
BUILDLINK_TRANSFORM+= rm:-DWITH_POSIX_TIMER
The FreeBSD-related PR you linked to enables Linux epoll emulation for
a specific code path.
If you want to test if that code path is reached, edit the
"os specific implementation is missing" messages in
work/freerdp-2.1.2/winpr/libwinpr/synch/timer.c.
Note that there are two such messages, and both are identical.
It would be useful to know which one is being triggered.
It's possible we need to either:
1) Enable the "__APPLE__" code paths in that file on NetBSD too.
2) Borrow the epoll emulation code.
I can't test this because I don't have a Windows machine to connect
to...