[clang] [Clang][Builtin] add __builtin_exit (PR #74803)

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W-50243 wrote:

I added __builtin_exit() because __builtin_exit() was used in some projects when I switched from GCC to LLVM. I don't think this is an isolated case, because the __builtin_exit() function is still widely used.[https://sourcegraph.com/search?q=context:global+__builtin_exit&patternType=standard&sm=1&groupBy=repo](https://sourcegraph.com/search?q=context:global+__builtin_exit&patternType=standard&sm=1&groupBy=repo)

https://github.com/llvm/llvm-project/pull/74803