Fix bugzilla 24592 - ImportC: Bitfield layout wrong for int64 on 32-b…

[tim-dlang]

…it Linux

Type ulong is 64-bit on 32-bit Linux, but has 32-bit alignment. This affects the layout of bitfields.

Also add a new test for ImportC bitfields, which compares size, alignment and layout with the host C++ compiler. The existing tests compared with fixed values instead.

[dlang-bot]

Thanks for your pull request and interest in making D better, @tim-dlang! 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

Auto-close	Bugzilla	Severity	Description
✓	24592	normal	ImportC: Bitfield layout wrong for int64 on 32-bit Linux

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 + dmd#16590"

[kinke]

Thanks a lot man for these real tests! They have uncovered an apparent AArch64-specific special case (except for Apple targets), see ldc-developers/ldc#4707 (comment) and following.