Rollup merge of #124281 - RalfJung:win-tls, r=joboet

fix weak memory bug in TLS on Windows

We need to store the `key` *after* we register the dtor.

Now I hope there isn't also some other reason why we have to actually register the dtor last... `@joboet` is there a reason you picked this particular order in rust-lang/rust#102655?

Fixes rust-lang/rust#123583