[Fix #11850] Build dependencies of build tool on disk too

[Saizan]

This PR fixes #11850 by taking the simple approach of ensuring the build tool can be properly built.

Checklist:

• Patches conform to the coding conventions.
• Any changes that could be relevant to users have been recorded in the changelog.
  • Is the change significant? If so, remember to add significance: significant in the changelog file.
• The documentation has been updated, if necessary.
• Manual QA notes have been included.
• Tests have been added. (Ask for help if you don’t know how to write them! Ask for an exemption if tests are too complex for too little coverage!)

[Mikolaj]

Thank you for the PR. Please mention the issue it fixes in the PR descriptions and please mark the PR with review_needed label once ready.

[Mikolaj]

Oh, and please add the changelog snippet.