Attempt to create a filesystem lock in the specified directory.

This will use OS-specific file locking primitives: GHC.IO.Handle.Lock with base-4.10" and later or a shim for base@ versions.

Throws an exception if the lock is already present.

May fallback to locking via creating a directory: Given a file pathto, we do this by attempting to create the directory /pathto/hackage-security-lock, and deleting the directory again afterwards. Creating a directory that already exists will throw an exception on most OSs (certainly Linux, OSX and Windows) and is a reasonably common way to implement a lock file.