This is to ensure that calls to `setjmp(3)` result in correct code
generation that respects `setjmp(3)`'s `returns_twice` behavior.
Otherwise, we might run into bugs (for example, Clang may perform
tail-call optimization on this function if `-fno-builtins` is set
(#122840)).
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Co-authored-by: Nick Desaulniers <nick.desaulniers@gmail.com>
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