Makefile: Don't read COMMIT, BUILDTAGS, EXTRA_BUILDTAGS from env vars

[rata]

We recently switched VERSION to be read from env vars (#4270). This
broke several projects, as they were building runc and using a VERSION
env var for, e.g. the containerd version.

When fixing that in #4370, we discussed to consider doing the same for
these variables too
(#4370 (review)).

Let's stop reading them from env vars, as it is very easy to do it by
mistake (e.g. compile runc and define a COMMIT env var, not to override
the commit shown in runc --version) and users that want can still
override them if they want to. For example, with:

    make EXTRA_BUILDTAGS=runc_nodmz

[kolyshkin]

LGTM

[thaJeztah]

🙈 needs a rebase

[rata]

Rebased now :)

[cpuguy83]

Wait... this now breaks builds again.

[cpuguy83]

There is no way to set a COMMIT except by carrying a patch to overwrite this.
It is removing something that has been in the Makefile for years.

Keep in mind that most of the time packagers do not have a .git to read from.

[tianon]

Doesn't make COMMIT=foo still work with this change?

[cpuguy83]

Oh yes, you are right. I always forget that make args can set those vars even without ?=. So I guess no patch is needed.

[akhilerm]

Oh yes, you are right. I always forget that make args can set those vars even without ?=. So I guess no patch is needed.

No patch is needed. I am building internally using

make EXTRA_VERSION=${version_meta} EXTRA_BUILDTAGS=${extra_build_tags} COMMIT=${runc_commit}

[thaJeztah]

Yeah, it's easy to confuse order;

This takes SOME_VAR from environment variables (which may, or may not work, depending on whether make is running in POSIX mode);

SOME_VAR=foo make some-target

This sets the make var;

make SOME_VAR=foo some-target

I got bit by that because macOS and Linux make differ, so now always default to the latter form 😅