The explain_fchdir_or_die function is used to change directory via
the fchdir(2) system call.
On failure, it prints an error message on
stderr via explain_fchdir(3), and exits.
This function is intended to be used in a fashion similar to the
following example:
explain_fchdir_or_die(fildes);
fildes
exactly as to be passed to the fchdir(2) system call.