[clang] [llvm] [SystemZ] Add support for __builtin_setjmp and __builtin_longjmp (PR #116642)

[Ulrich Weigand via cfe-commits]

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+; -mbackchain option.
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uweigand wrote:

Also, I don't think we need -mbackchain versions of all of those.   We have the simple tests above that verify -mbackchain works, we don't need to repeat this for all other tests.

https://github.com/llvm/llvm-project/pull/116642