chg: extract the logic of setting FD_CLOEXEC to a utility function Setting FD_CLOEXEC is useful for other fds such like lockfd and sockdirfd, move the logic from hgc_open to util.

chg: add fchdirx as a utility function As part of the series to support long socket paths, we need to use fchdir and check its result in several places. Make it a utility function.