[llvm] [llvm] Introduce XROS platform (PR #77707)

[Cyndy Ishida via llvm-commits]

cyndyishida wrote:

> LGTM. The formatting issues are the result of the surrounding code not being compliant. Personally don't think it's worth the churn but even if it were that's something to be fixed in a separate PR.

Correct. I feel like the right thing is to add `/* clang-format off */` around these offending code regions but can be handled in separate PR depending on how others feel. 

https://github.com/llvm/llvm-project/pull/77707