[PATCH] Avoid dlopen on debuginfod-client when not configured

[Frank Ch. Eigler]

Hi -

> > Avoid dlopen() when no debuginfo url is set.
> 
> The patch itself looks right. But I am slightly afraid this
> (theoretically?) will break some programs which set DEBUGINFOD_URLS
> themselves. We currently have no other way to make libdwfl use
> debuginfod-client. Thoughts?

I've been thinking that doing all this dlopen work in the real dwfl
function(s) rather than the solib ctor would be fine.

- FChE