Overwrite instead of adding to archives when creating them in mri scripts.

This matches the behavior of GNU ar and also makes it easier to implemnt
support for the addlib command.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220336 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed