Conditionalized OsLogger.cpp on a modern SDK.
Conditionalized OsLogger.cpp on a modern SDK.

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@293020 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit c155dbbbb1f41d2fec557098a2e8311c92f6d585)

apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb