[boost] cygwin API: posix or windows

Hi, while trying to make Boost.System and Boost.Chrono configurable header only libs we need to include windows.h on some include files. To avoid the inclusion of this intrusive file, we decided sometime ago to include some files in detail/win that will present just the needed interfaces. In my humble opinion cygwin is a wrapper of posix intefaces under windows OS. So, boost libraries shouldn't use Windows interfaces when working under cygwin. What's the experience of others? Best, Vicente