Fix PathMappingListTest on windows
Fix PathMappingListTest on windows

r334615 changed the the value of FileSpec.IsRelative("/") for windows
path syntax. We previously considered it absolute but now it is
considered relative (I guess because it's interpretation depends on the
current drive).

This cause a failure in PathMappingList test, which assumed that "/"
will not get remapped as it is an absolute path. As this is no longer
true on windows, I replace "/" with a really absolute path.

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@334702 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb,apple/swift-lldb,llvm-mirror/lldb