[llvm] [cmake] Fix overlapping native llvm-min-tblgen builds (PR #121021)

[Mehdi Amini via llvm-commits]

https://github.com/joker-eph approved this pull request.

Isn't this fragile? The build system allows multiple invocation of subprocess builds in the native folder.
Isn't there a way to present this?

https://github.com/llvm/llvm-project/pull/121021