The pthread wrapper for Windows compiled on 64-bit, not on 32-bit Windows.

Compilation of librist failed on Windows with Visual Studio 2019.

Move flow shutdown before lock to fix rare locking issue where lock never gets acquired while output thread
keeps locking/unlocking.

Restarting a rist2rist source sometimes causes the receiver
connected to rist2rist to break because it never recalculates
the time offset.
Reset the flow if we go over a late packets threshhold.

If not, pkg-config produces a file that contains a full path
to libwinpthread.a

Signed-off-by: Christopher Degawa <ccom@randomderp.com>

Weights of chosen peers were not correctly being subtracted in this case.

Per packet messages where flooding a system, creating a unrecoverable situation.
Flushing data earlier when real time spend in buffer exceeds 1.1 * buffer duration
ensure that it's more likely to be useful.
We can then also safely drop any stale packets we find that are there longer than 2
buffer durations (there shouldn't be any).

* initialize variable we check against before any jumps to cleanup
* use boolean to indicate thread startup, instead of incorrectly
  checking against pthread_t

Also keep sending to dead peers till at least the buffer recovery period has expired (their downstream might still be functional, while their upstream has broken)
Fixes #115

Set these options manually for the old behavior of building
cjson and mbedtls as part of the library. Otherwise you'll
need to have working pkg-config/cmake tooling for finding
these dependencies.

Fixes #111

Replace current win32 poll emulation function with another one with an open domain license from the libressl-portable project.
It was brought to our attention that the current function was derived from VLC's code and the LGPL license on it is not compatible with our BSD2 license.