[PATCH] D40606: [Support/TarWriter] - Don't allow TarWriter to add the same file more than once.

[George Rimar via llvm-commits]

>The code change LGTM.
>
>The TarWriter is tested in llvm with unittests. Can you add a test
>showing that if the same path is added twice we only keep the first one?
>
>Thanks,
>Rafael

Updated diff, added testcase. It checks tar file size do not change when we add
multiple files for the same path. Do it checks only one file is used, but does not check
which one. Looks it is fine for now ?

George.