Makefile: replace mergemaster references with etcupdate

[driesm]

Summary

Similar to UDPATING and handbook changes, treat Makefile the same.

[imp]

I think this is good, but I added @jhb to make sure

[philip]

Thanks! This looks good but please add a note about bootstrapping etcupdate. I always forget about etcupdate extract on new development machines.

A brief mention of 'remember to bootstrap etcupdate if necessary' before make buildworld would go a long way!

[philip]

(It should go *before* make buildworld because etcupdate extract needs to be done with the source tree of the *running* system. I've been bitten multiple times by "oh rats; git checkout freebsd/release/XXX; etcupdate extract; git checkout main; make installworld and finding that installworld fails because Git changed timestamps.)

[jhb]

In D36877#837255, @philip wrote:

Thanks! This looks good but please add a note about bootstrapping etcupdate. I always forget about etcupdate extract on new development machines.

A brief mention of 'remember to bootstrap etcupdate if necessary' before make buildworld would go a long way!

Note that you don't need to bootstrap on machines installed from a release since about 9.0. The release media already bootstraps etcupdate so bootstrapping should mostly not be a thing on modern installs.

[driesm]

I'm from the opinion to keep this instruction as simple as possible.
The handbook has some extra steps for switching from mergemaster to etcupdate where an "etcupdate extract" is required.
As @jhb pointed out, bootstrapping should not be required for any recent release.

I would like to push as is. If we would add an extra note, I think UPDATING is more appropriate location then Makefile to add these edge cases.

Thoughts?

[philip]

@jhb: that's odd ... etcupdate -p failed for me last week after building main on 13.1 as described in my earlier comment. Perhaps I messed something else up. I'll try to reproduce and narrow it down.

I agree with @driesm about keeping this simple. Since it looks like my problem is likely unrelated, I'm good with this being pushed as-is.