[clang] [Clang][Builtins] Support typedefs and struct tags in LibBuiltin prototypes (PR #231696)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

I'd be okay with introducing some form of "weak" builtin, where we model the call as a builtin function while only doing some approximate verification of the signature.

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I think this patch is missing serialization bits.  CC @ChuanqiXu9

https://github.com/llvm/llvm-project/pull/231696