STL_MSFT marked an inline comment as done.
> This approach looks good to me.
> Is there any chance we could have a test for this?
Unfortunately, testing this involves having a VS toolset with the DevDiv-internal directory structure. Preparing that is a laborious manual process, and requires installation of the Windows SDK (I sent repro instructions to cfe-dev). Even given a real installation of VS, I don't think I could write automated test code to extract a copy with the necessary directory structure (doing so would almost involve replicating the codepaths being touched here). But now that I know that this code exists and that Clang occasionally changes it, especially in response to new VS directory structures, I'll watch for new betas/RCs and verify them against our internal builds.