Could avoid querying pkg-config with multiple times the same package

[elmarco]

There is a regression in pkgconf which breaks system-deps: https://github.com/pkgconf/pkgconf/issues/310

Could system-deps be a bit more clever and avoid querying multiple times the same package?

[gdesmott]

I don't understand how this regression can break system-deps, do you have an example?

Tbh I won't have time to look at this for a while, but I'm happy to merge and release a fix if someone can provide a PR.