[boost] Cygwin patches

Hi, I've created a set of patches that together allow boost to build on cygwin. - https://github.com/boostorg/asio/pull/463 - https://github.com/boostorg/context/pull/322 - https://github.com/boostorg/process/pull/533 - https://github.com/boostorg/stacktrace/pull/219 - https://github.com/boostorg/system/pull/137 I also made a tracking issue with links to all of them: - https://github.com/boostorg/boost/issues/1112