mingw fixes (backport #12298)

[mergify]

Motivation

The build is failing: https://hydra.nixos.org/build/285623585

Context

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This is an automatic backport of pull request #12298 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of c656725 has failed:

On branch mergify/bp/2.24-maintenance/pr-12298
Your branch is up to date with 'origin/2.24-maintenance'.

You are currently cherry-picking commit c656725a1.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   src/libutil/posix-source-accessor.cc

no changes added to commit (use "git add" and/or "git commit -a")

Cherry-pick of d863684 has failed:

On branch mergify/bp/2.24-maintenance/pr-12298
Your branch is ahead of 'origin/2.24-maintenance' by 1 commit.
  (use "git push" to publish your local commits)

You are currently cherry-picking commit d8636843b.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   packaging/dependencies.nix

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally