use DESTDIR in Makefile for debian

[joshrabinowitz]

This is part of #386

The TL;DR:

We should probably be installing into $DESTDIR/$PREFIX

Details:

According to the Debian Upstream Guide https://wiki.debian.org/UpstreamGuide we should be using DESTDIR (they don't mention PREFIX)

Installation
Please honor the DESTDIR environment variable or make variable and use its contents as a prefix in front of all installation paths. ...

Gnu coding standards agree at https://www.gnu.org/prep/standards/html_node/DESTDIR.html

DESTDIR is a variable prepended to each installed target file, like this:

$(INSTALL_PROGRAM) foo $(DESTDIR)$(bindir)/foo
$(INSTALL_DATA) libfoo.a $(DESTDIR)$(libdir)/libfoo.a

The DESTDIR variable is specified by the user on the make command line as an absolute file
name. For example:

make DESTDIR=/tmp/stage install

FreeBSD docs at https://www.freebsd.org/doc/en_US.ISO8859-1/books/porters-handbook/porting-prefix.html give even more details:

PREFIX determines where the port will be installed. It defaults to /usr/local, but can be set by the user to a custom path like /opt. The port must respect the value of this variable.

DESTDIR, if set by the user, determines the complete alternative environment, usually a jail or an installed system mounted somewhere other than /.

[joshrabinowitz]

@sobolevn @simbo1905 Please let me know if you have thoughts about this issue.

[simbo1905]

Seems like a good idea. Will it effect fedora and alpine?

[joshrabinowitz]

@simbo1905 they actually document cases where it works just as it does in Debian:

https://wiki.archlinux.org/index.php/creating_packages indicates that arch linux expects it to work as debian does,

https://fedoraproject.org/wiki/Archive:PackagingDrafts/MakeInstall indicates Fedora is the same.

Edit: Repeated point removed apparently it's a GNU thing: https://www.gnu.org/prep/standards/standards.html#DESTDIR

[joshrabinowitz]

https://nullprogram.com/blog/2017/08/20/ also talks about DESTDIR and PREFIX both being makefile conventions.
The article also shows an example of a program being installed in $(DESTDIR)$(PREFIX)/bin