[llvm-branch-commits] [FileSystem] Allow exclusive file lock (PR #114098)

[Steven Wu via llvm-branch-commits]

https://github.com/cachemeifyoucan created https://github.com/llvm/llvm-project/pull/114098

Add parameter to file lock API to allow exclusive file lock. Both Unix
and Windows support lock the file exclusively for write for one process
and LLVM OnDiskCAS uses exclusive file lock to coordinate CAS creation.