Compute the path properly on different platforms. Specifically, compute it the exact same way that the Clang code computes this path.
Compute the path properly on different platforms. Specifically, compute
it the exact same way that the Clang code computes this path.

Hopefully with this, the MSVC bots will actually come back to life.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@143807 91177308-0d34-0410-b5e6-96231b3b80d8

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