[llvm] [cmake] Preserve CMake file API queries when clearing an LLVM external project build directory (PR #206801)

[Petr Hosek via llvm-commits]

petrhosek wrote:

> > When clearing the build d9irectory, I would want a fresh start, including not having such outdated queries preserved.
> 
> The problem is that the build system will clear the build directory for you depending on the stamps, and when that happens your IDE support gets clobbered with it and you have to set it all back up by hand which is a real pain. There's nothing outdated in the queries, it's the replies that are outdated and those aren't preserved.

What's the purpose of these queries? Why do we need to preserve them?

https://github.com/llvm/llvm-project/pull/206801