[llvm] [llvm][Support] Call clear_error in LockFileManager to avoid report_fatal_error (PR #83655)

[Michael Spencer via llvm-commits]

Bigcheese wrote:

Yeah, this was just for CI, I'll add the tag in the future.

Getting into a situation that would have an error here is the hard part. I don't actually know how it happened, all I have is a stack trace from the call to `abort` after `report_fatal_error`, but not the actual error it failed with. To get here you have to successfully create and open the lock file with the correct permissions, but then fail to write to it. It's possible this happened because of a network failure or some other weird situation.

https://github.com/llvm/llvm-project/pull/83655