rfc/patch: user-agent distro-description for debuginfod http traffic

[Frank Ch. Eigler]

Hi -

> > > We do want a reproducible build. 
> > 
> > Can you give an example?  Bootstrapping a new distro version/arch?
> 
> Probably best explained at https://reproducible-builds.org/ most
> distributions are participating.

(I understood that part, just not how you thought build-time literals
would break reproducibility.)

> It looks like an easily parsable file format.  The attached produces
> some reasonable looking identification strings on a couple of my
> systems out of the box:

OK, took your code, tweaked it just a touch, confirmed it's valgrind
leak-free, and merged to master.

- FChE