[libstdc++] Update comments in testsuite files, add dummy tool file.

[Benjamin Kosnik]

>| No, I think /we/ got the wrong file name, back when all this was put
>| into place.
>
>Hmm, when I put the DejaGnu testing framework into place, the file was
>named libstdc++.exp.  It got renamed to the current name after some
>complete rewrite. 

Probably my fault.

> If people don't mind, sure, I'll rename it after the autotools transition.

Sounds like a good plan.

-benjamin