Auto-fill the `MAKE` variable.

[gregschmit]

We should add MAKE as a special key for the Vars struct (much like .RECIPEPREFIX and set it to however the current program was invoked.

[xadaemon]

This one has quite a bit of detail to it, GNU docs.

extra link:
https://www.gnu.org/software/make/manual/html_node/Recursion.html

[xadaemon]

You can assign me this one, I should have time to work on it this week

[gregschmit]

Awesome; thank you! Let me know if you have any questions.

[xadaemon]

I got around to working on this one, I will implement it as the GNU docs specify, I will also add a rudimentary impl of the MAKEFLAGS variable.