[clang] [clang] UEFI ABI fixes for X86_64 (PR #124992)

[via cfe-commits]

Prabhuk wrote:

Besides the places I have updated "isOSWindows()" with "isWindowsOrUEFI()", there are quite a few occurrences of isOSWindows() checks within Clang code. Which one of these must be included to make sure the mangling and other ABI related decisions made for X86_64 UEFI targets are done correctly?

https://github.com/search?q=repo%3Allvm%2Fllvm-project+path%3A%2F%5Eclang%5C%2F%2F+isOSWindows%28%29&type=code

https://github.com/llvm/llvm-project/pull/124992