[llvm] [Support] Restrict ManagedStatic ThreadPoolExecutor to Windows (PR #102989)

[Fangrui Song via llvm-commits]

MaskRay wrote:

> I've been on PTO, but this LGTM. Only comment is that the mention of other threads accessing TLS objects reads a bit odd. IIUC, isn't the issue related to the fact that other threads access objects allocated by a different thread local allocator?

Yes, the issue was due to threads access objects allocated by a different thread local allocator. The objects might be destroyed TLS destructors.

https://github.com/llvm/llvm-project/pull/102989