general to be of much use. Using it here weakened the _PC_MAX_CANON,
_PC_MAX_INPUT and _PC_VDISABLE cases.
fifo_pathconf() is not quite correct either. _PC_CHOWN_RESTRICTED
and _PC_LINK_MAX should be handled by the host file system. For
directories, the host file system should let us handle _PC_PIPE_BUF.