Let's run arbitrary code downloaded from somewhere I don't know! As root!

Did you read the linked Makefile?

1. The posted code could change between when you read it and when I read it.

2. If you just cut-and-paste these three lines, then you are obviously not reading it.

That's why you have another line saying something like:

    cat Makefile

before blindly executing it. In general, you shouldn't blindly believe downloaded code, but in this case Makefile is simple enough that you can prove it's non harmful in a few second glance.