Completion: Add make variables with values

[mstaz]

So far only variable names were added. However Makefiles and make would also return possible values which are not completed so far. The values are stored and overwritten in the map without using them anywhere. So instead it currently makes more sense to complete the whole variable name-value combination instead of only the name.

I'm unsure about this change because I have not completely understood zsh's completion system yet. However it works for me (version 5.8 and call-command set true) as I want it to be. It's similar to bash's behavior with that.

[larryv]

This contribution should probably be discussed on the mailing list, since it significantly changes completion behavior. Very few committers monitor this repository mirror, and little to no discussion happens here.

[mstaz]

Thanks for the advice. I followed zsh-completions/CONTRIBUTING.md which states that completion functions can be contributed via github pr as well. But maybe you are right.

[okdana]

we do accept completion contributions via pr, it's just that in this case it would be a controversial change

i don't find it desirable at all to complete the entire variable=value pair and i doubt others will either. it makes it very annoying in the most common case where you just want to assign your own value

what we could do instead is offer values parsed out of the file as possibilities if you complete like VAR=<TAB>. i didn't study it closely but as you mentioned the ground-work for this already exists in the function, it just isn't exposed. that would be inoffensive imo