Always set the mode.

This matches GNU ar behavior. Also remove the now unused getFileStatus method.
Not sure how to add a test, it would have to run ls -l or something like that.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184337 91177308-0d34-0410-b5e6-96231b3b80d8