[llvm] [Xtensa] Implement Xtensa S32C1I Option and atomics lowering. (PR #137134)

[Fangrui Song via llvm-commits]

MaskRay wrote:

> Implement Xtensa S32C1I Option and use s32c1i instruction to implement atomics operations.

Can use a more elaborated comment to help future readers :) Not just copy the patch title

https://github.com/llvm/llvm-project/pull/137134