[PATCH] config: Conditionalize on LIBDEBUGINFOD instead of DEBUGINFOD

[Frank Ch. Eigler]

Hi -

> That is a good point. But I think the default setting is wrong if it
> isn't actually used/setup. As the profile shell snippets are now they
> define the DEBUGINFOD_URLS environment variable as an non-empty string
> (although just containing spaces), [...]

Good point, we should make it empty or unset in that case.  Will send
a shell scripting patch to the profile files.

- FChE