add `extra-args` to file comments

[c-cube]

in a given benchmark, need # extra-args(zipperposition): --arith and the likes to customize the command line of a prover on this file?

[Gbury]

I'm not so sure about that. My point of view is the following:

• either the extra arg doesn't impact performances when it is not effectively used, and it can be added to the command line of the prover
• or it does impact performance, and then it is all the more reason to specify it on the command line in order not ot hide the costs related to it, or the tool should be able to automatically detect when it should be used

However, these points are heavily influenced by my usage of frogutils to perform benchs, I agree that for tests, adding arguments on the fly seems reasonable.

[c-cube]

It's not for performance, it's for simply working at all…