bug#59503: 28.2.50; cannot set --mandir when installing

[Eli Zaretskii]

> Date: Wed, 23 Nov 2022 12:11:55 +0700
> From: daanturo <daanturo@gmail.com>
> 
> Despite having set --prefix and/or --mandir to a writable directory in
> my $HOME, `make install` always throws me this:
> 
> /usr/bin/mkdir: cannot create directory ‘/usr/local/share/man/man1’: 
> Permission denied

Please show the complete Makefile from the top-level directory of the tree
where you built Emacs.

AFAICT, the command to create that directory is

        umask 022; ${MKDIR_P} "$(DESTDIR)${man1dir}"

and ${man1dir} is determined as follows:

  datarootdir=${prefix}/share
  mandir=${datarootdir}/man
  man1dir=$(mandir)/man1

So if you set prefix to some directory, man pages should be installed in the
share/man/man1 subdirectory of that directory, not in
/usr/local/share/man/man1.  Something's amiss here.