[bug#45692] [PATCH v3 2/3] gnu: Add zfs-auto-snapshot.

[raid5atemyhomework]

Hello Danny,

> Hi,
>
> > -                  (invoke "make" "install"
> >
> >
> > -                          "PREFIX="
> >
> >
> > -                          (string-append "DESTDIR=" out)))
> >
> >
>
> Are you sure about that?
>
> Usually, DESTDIR is in order to supply a temporary build root (which will not
> be referred-to by the installed programs--because that directory will be
> deleted after the build) and PREFIX is in order to supply an actual
> installation directory (installed programs can refer to that whenever they
> want).
>
> Is it different for this program?
>
> Also, I'd suggest to use #:make-flags so other phases can also see the PREFIX
> chosen. Otherwise, those could erroneously default to another prefix (for
> loading of config files at runtime etc).
>
> What do you think?

Yes, I am quite sure; the program uses a custom `Makefile` that is fairly 
simple and can be trivially quoted here for your review:

```Makefile
PREFIX := /usr/local

all:

install:
        install -d $(DESTDIR)/etc/cron.d
        install -d $(DESTDIR)/etc/cron.daily
        install -d $(DESTDIR)/etc/cron.hourly
        install -d $(DESTDIR)/etc/cron.weekly
        install -d $(DESTDIR)/etc/cron.monthly
        install -m 0644 etc/zfs-auto-snapshot.cron.frequent 
$(DESTDIR)/etc/cron.d/zfs-auto-snapshot
        install etc/zfs-auto-snapshot.cron.hourly   
$(DESTDIR)/etc/cron.hourly/zfs-auto-snapshot
        install etc/zfs-auto-snapshot.cron.daily    
$(DESTDIR)/etc/cron.daily/zfs-auto-snapshot
        install etc/zfs-auto-snapshot.cron.weekly   
$(DESTDIR)/etc/cron.weekly/zfs-auto-snapshot
        install etc/zfs-auto-snapshot.cron.monthly  
$(DESTDIR)/etc/cron.monthly/zfs-auto-snapshot
        install -d $(DESTDIR)$(PREFIX)/share/man/man8
        install -m 0644 src/zfs-auto-snapshot.8 
$(DESTDIR)$(PREFIX)/share/man/man8/zfs-auto-snapshot.8
        install -d $(DESTDIR)$(PREFIX)/sbin
        install src/zfs-auto-snapshot.sh 
$(DESTDIR)$(PREFIX)/sbin/zfs-auto-snapshot

uninstall:
        rm $(DESTDIR)/etc/cron.d/zfs-auto-snapshot
        rm $(DESTDIR)/etc/cron.hourly/zfs-auto-snapshot
        rm $(DESTDIR)/etc/cron.daily/zfs-auto-snapshot
        rm $(DESTDIR)/etc/cron.weekly/zfs-auto-snapshot
        rm $(DESTDIR)/etc/cron.monthly/zfs-auto-snapshot
        rm $(DESTDIR)$(PREFIX)/share/man/man8/zfs-auto-snapshot.8
        rm $(DESTDIR)$(PREFIX)/sbin/zfs-auto-snapshot
```

Notice how it does not modify any of the source files at all, so the sources do 
not refer to anything provided in `$PREFIX`.  However, it does create 
directories in `$DESTDIR`, so it has to use `$DESTDIR`.

Thanks
raid5atemyhomework