[Support] remove_dots: Remove .. from absolute paths.

/../foo is still a proper path after removing the dotdot. This should
now finally match https://9p.io/sys/doc/lexnames.html [Cleaning names].

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@284384 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed