[llvm] [clang] [clang-tools-extra] [clang] Refactor Builtins.def to be a tablegen file (PR #68324)

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https://github.com/michele-scandale commented:

I've found few differences w.r.t. the previous builtins definition. If the change was intended to be a NFC then they might be considered issues.

https://github.com/llvm/llvm-project/pull/68324