[clang-tools-extra] Fix Default Asset File locator for clang docs (PR #97505)

[Justin Bogner via cfe-commits]

https://github.com/bogner approved this pull request.

It's kind of unfortunate how this works dependency-wise - we end up creating "Debug/share/clang-doc/${f}" even when we only build "Release" and vice-versa, as the "copy-clang-doc-assets" explicitly depends on each version of this file. Also the actual install copies the file directly from the source directory, so if we did end up actually configuring these files per config for some reason there's some potential for confusion.

However, the cmake-fu to do this any better is beyond me, and the current state is that we actually have broken bots because of this, so I think the solution here is Good Enough to get in and get the bots unblocked.

https://github.com/llvm/llvm-project/pull/97505