[CAS] Sync LLVMCAS library implementation to next#12794

cachemeifyoucan wants to merge 6 commits intoswiftlang:stable/21.xswiftlang/llvm-project:stable/21.xfrom

cachemeifyoucan:eng/PR-sync-cas-next-to-21.xcachemeifyoucan/llvm-project:eng/PR-sync-cas-next-to-21.xCopy head branch name to clipboard