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

[Nikolas Klauser via cfe-commits]

philnik777 wrote:

I'm not really convinced that `__builtin_exit` is widely used. If you filter for C/C++ and exclude GCC there aren't many matches: https://sourcegraph.com/search?q=context:global+__builtin_exit+count:all+-file:gcc/.*+%28lang:C+OR+lang:C%2B%2B%29&patternType=standard&sm=0&groupBy=repo

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