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

[Eli Zaretskii]

> From: Jonas Bernoulli <jonas@bernoul.li>
> Date: Sun, 25 Sep 2022 21:09:41 +0200
> 
> On Guix pwd isn't located at /bin/pwd, but that path is hard-coded in
> various Makefile.in.  They deal with that by patching these files when
> building the emacs package, but when building emacs manually, that isn't
> convenient, as doing so would leave the working tree dirty, which makes
> it harder to pull whenever one of these files changes.
> 
> Please consider making this customizable so one could use, for example:
> 
>   make PWDCMD=pwd install
> 
> I assume there is a reason why the PWD variable isn't being used and
> that /bin/pwd is used because on some other OS using pwd would cause
> issues.

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?