[llvm] [Xtensa] Implement Xtensa Region Protection Option and several other small Options. (PR #137135)

[Fangrui Song via llvm-commits]

MaskRay wrote:

We ensure that llvm-project compiles without any warning with a recent Clang, but the latest the latest Xtensa target has some warnings.

I typically use this prebuilt Clang from chromium
 https://raw.githubusercontent.com/chromium/chromium/main/tools/clang/scripts/update.py 

https://github.com/llvm/llvm-project/pull/137135