Fix Issue 19563 Fix extern(C++) Incorrect ABI passing small struct

[ghost]

Patched #9295

[dlang-bot]

Thanks for your pull request and interest in making D better, @look-at-me! 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 annotated coverage diff directly on GitHub with CodeCov's browser extension
• 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

Auto-close	Bugzilla	Severity	Description
✓	19563	blocker	extern(C++) Incorrect ABI passing small struct

⚠️⚠️⚠️ Warnings ⚠️⚠️⚠️

• Regression or critical bug fixes should always target the stable branch. Learn more about rebasing to stable or the D release process.

To target stable perform these two steps:

1. Rebase your branch to upstream/stable:

git rebase --onto upstream/stable upstream/master

2. Change the base branch of your PR to stable

Testing this PR locally

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

dub fetch digger
dub run digger -- build "master + dmd#9434"

[thewilsonator]

Could you please break up some of those monster expressions?

[ghost]

The CircleCI failure seems to be unrelated (is happening in other PRs) and the buildkite failure is because it ran out of memory building druntime..

[wilzbach]

and the buildkite failure is because it ran out of memory building druntime..

To be more specific this happens when trying to build the benchmark-compile-only target:

Segmentation fault (core dumped)
--
  | posix.mak:336: recipe for target 'benchmark-compile-only' failed

[ghost]

:/ it'd be nice if it reprinted the failure at the end

[ghost]

@wilzbach
Looks like it is using the new compiler to build runbench.d but it hasn't built the new phobos and it is using a different version of phobos (the preinstalled one?). Not sure how you want to go about fixing that, would need to change the config for build-kite and how it builds/tests druntime.

[thewilsonator]

I seem to remember having "fun" with the benchmarking before. Given Circle seems to fail with some unrelated GDB I'm in favour of merging this.

[CyberShadow]

This pull request introduced a regression:
https://issues.dlang.org/show_bug.cgi?id=23901