Makefile: don't align variable definitions.

This makes the Makefile much more readable 

1. No need to scour the variable definition at the other end of the page. This is especially bad for the sequence of variables `0` and `1`, where you loose track of the line and somehow need your finger to keep track of the line. 

2. Run much less quickly in the 80 columns limit, which makes it more readable in terminals. 

(Side note I have see a trend among programmers to align a lot their code, while it makes a good *impression* I'm not sure it's a good idea. The above arguments apply but also from a code maintenance point of view if you introduce a longer case then you need to realign everything => the patch becomes longer => it's longer to review even though essentially few things changes, the patch no longer gives the essence of the change. The OCaml programming guidelines actually explicitly say you should not try to align things like arrows in pattern cases)