osutil: disable compilation of recvfds() on unsupported platforms It appears that Solaris doesn't provide CMSG_LEN(), msg_control, etc. As recvfds() is only necessary for chg, this patch just drops it if CMSG_LEN isn't defined, which is the same workaround as Python 3.x. https://hg.python.org/cpython/rev/c64216addd7f#l7.33