[libc-commits] [libc] [libc][NFC] Move `BigInt` out of the `cpp` namespace (PR #84445)

[Clement Courbet via libc-commits]

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

Indeed it makes more sense for BitInt to be outside of `cpp`.

https://github.com/llvm/llvm-project/pull/84445