Should the linter warn if a package depends on multiple versions of the same program?

[Leo Famulari]

Currently we have a problem caused by glibmm-2.64 propagating two
different versions of libsigc++:

https://issues.guix.gnu.org/52519

I think this is something that is rarely desirable.

Maybe the linter could check for cases like this? Of course, "cases like
this" still needs to be defined exactly...