Makefile: Allow prefix to be set from outside

[LeSpocky]

This way external build systems can override prefix and decide to not install into $HOME.

Fixes: c11923a ("make: add install and uninstall targets")

[felipec]

You can just do make prefix=/usr, that overrides the variable: overriding variables.

[LeSpocky]

You can just do make prefix=/usr, that overrides the variable: overriding variables.

Nice to know. The conditional variable assignement makes it a little more flexible, because make can also take the value from the environment then.

[felipec]

@LeSpocky if you want the environment to override variables, you should use make -e. ?= is more commonly used when dealing with multiple Makefiles including each other.

[LeSpocky]

You can just do make prefix=/usr, that overrides the variable: overriding variables.

I checked packages in buildroot this morning and found this is actually a common way to set prefix from outside. Not sure why my brain suggested the other way?! Calling make prefix=/usr install now and that works. Sorry for the noise.

[felipec]

No problem. It took me a while to figure out all the common ways Makefiles are used, but yeah make prefix=/usr install is pretty common.

For reference this is what I use in my Arch Linux package:

DESTDIR="$pkgdir" make prefix=/usr VIM_DIR=/usr/share/vim/vimfiles install install-vim