Fix issue 18063 - thread_attachThis returns dangling pointer

[Temtaime]

Rebase of #1989

[dlang-bot]

Thanks for your pull request and interest in making D better, @Temtaime! We are looking forward to reviewing it, and you should be hearing from a maintainer soon.
Please verify that your PR follows this checklist:

• My PR is fully covered with tests (you can see the coverage diff by visiting the details link of the codecov check)
• My PR is as minimal as possible (smaller, focused PRs are easier to review than big ones)
• I have provided a detailed rationale explaining my changes
• New or modified functions have Ddoc comments (with Params: and Returns:)

Please see CONTRIBUTING.md for more information.

---

If you have addressed all reviews or aren't sure how to proceed, don't hesitate to ping us with a simple comment.

Bugzilla references

Your PR doesn't reference any Bugzilla issue.

If your PR contains non-trivial changes, please reference a Bugzilla issue or create a manual changelog.

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + druntime#3579"

[Temtaime]

@acehreli Thanks for your work, but
*** Error in `./generated/linux/release/64/attach_detach': free(): invalid pointer: 0x00007fa1a0002930 ***
What had i missed ?

[acehreli]

I worked on this PR without any prior experience with druntime after hitting similar or the same issues as you did. :) It is very likely that it's not complete. In fact, it used to fail the OSX 32-bit tests, which were special because thread-local storage was implemented (reportedly) manually there.

[acehreli]

I should add: The OSX 32-bit support has since been dropped, so I was hoping that the PR is in better shape but apparently not. :/