[clang] [clang] Introduce a new UEFI target predefine. (PR #111719)

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Prabhuk wrote:

> Didn't know this existed, but we have #120632 tracking it now.

Thanks. I left another comment there for @RossComputerGuy to decide on whether to land this patch or not.

https://github.com/llvm/llvm-project/pull/111719