bug#58080: 29.0.50; Don't hard-code path to pwd

[Gregory Heytings]

> I don't see anything like PWDCMD in any of the GNU projects I have here, 
> but they do use just "pwd", not "/bin/pwd".  So maybe so should we, and 
> that would solve this particular problem as well?

The difference is that /bin/pwd gives, unlike pwd, the "true" path 
(without symlinks).  Not sure if it's important enough to justify the use 
of /bin/pwd, though.  The use of /bin/pwd instead of pwd dates from 
8672a560f6 by RMS in 1994.