[v23.3.x] cmake: tweaks for vtools trunk-based development

[ivotron]

Needs to be merged after main is made the default branch in vtools so that builds against the 23.3.x branch work with the new trunk-based development model in vtools.

Manual backport of https://github.com/redpanda-data/redpanda/pull/19853. Done manually to have it ready to be merged right after the switch of vtools default branch

Backports Required

• [ ] none - not a bug fix
• [x] none - this is a backport
• [ ] none - issue does not exist in previous branches
• [ ] none - papercut/not impactful enough to backport
• [ ] v24.1.x
• [ ] v23.3.x
• [ ] v23.2.x

Release Notes

• none

[ivotron]

build that tests these changes is in https://buildkite.com/redpanda/redpanda-dev/builds/123. It's passing except from some flaky tests in ducktape that are irrelevant to the changes in this PR. The redpanda and bk-redpanda jobs can be ignored since they are running against vtool's dev