[llvm] [llvm-project][llvm] .gitignore supports filtering folders starting with cmake-build (PR #110649)

[Benoit Jacob via llvm-commits]

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

This looks reasonable to me, but I am not sure if I am an authorized reviewer for these files. FYI @joker-eph .

https://github.com/llvm/llvm-project/pull/110649