[clang] Fix an issue where clang++ and clangd uses enormous amounts of memory (PR #88637)

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

I'm not sure this is testable, but if you can think of a test, that would be nice.
Can you also add a release note to `clang/ReleaseNotes.rst`?

https://github.com/llvm/llvm-project/pull/88637