Make sure the solver sees the correct subdir

[jaimergp]

Description

Should fix #5341

Checklist - did you ...

• Add a file to the news directory (using the template) for the next release's release notes?
• Add / update necessary tests?
• Add / update outdated documentation?

[codspeed-hq]

CodSpeed Performance Report

Merging #5350 will not alter performance

_{Comparing jaimergp:cross-subdir (9867682) with main (01b47f4)}

Summary

✅ 3 untouched benchmarks

[mbargull]

WDYT about the question about the target branch (main vs 24.5.x) from #5341 (comment) :

As for when/how to include this:

1. We could include this in a 24.5.x patch release ("fixes cross-platform building with virtual packages"),
2. or include this only in 24.7.x ("adding support for proper cross-platform building").

In principle, I'd be in favor of option 1, but am also not sure if this could be an "unexpected environment resolving change for a patch release" for some.

[kenodegard]

Since this is a bugfix and not a regression I'm in favor of merging this into main and release with 24.7.x

[isuruf]

Thank you everyone for helping on this issue. Let's get this in for 24.7