Solution: use pthread API to set the name. For now call every thread
"ZMQ b/g thread". Would be nice to number the I/O threads and name
explicitly the reaper thread, but in reality a bit of internal API
churn would be necessary, so perhaps it's not worth it.
This is useful when debugging a process with many threads.

Solution: if available, use eventfd with EFD_CLOEXEC flag to make
the process close the socket on fork+exec

Solution: add macro in ZMQSourceRunChecks.cmake and optionally
include the TIPC sources if the support is available.
More importantly, only run the TIPC tests if the support is there.

Replace _zmq_COMPILER with CMAKE_VS_PLATFORM_TOOLSET; so the suffix can
be automagically generated for every MSVC compiler supported by cmake.