[llvm] [Support] On Windows, fix rpmalloc TLS destructor when running inside a DLL (PR #171465)

[Alexandre Ganea via llvm-commits]

https://github.com/aganea approved this pull request.

LGTM, thank you for the changes! Let's wait until next week before land this, in case there are other comments.

https://github.com/llvm/llvm-project/pull/171465