C++ small struct test

[TurkeyMan]

This unittest shouldn't fail, but there seems to be an ABI issue with small struct's, which needs to be fixed.

https://issues.dlang.org/show_bug.cgi?id=19563

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[TurkeyMan]

Don't jump to conclusions; I expect this to fail CI, and hopefully motivate someone to fix it ;)

[WalterBright]

I don't understand. If there's a bug that needs fixing, and this PR is not fixing, shouldn't it be in bugzilla instead?

[TurkeyMan]

The bugzilla issue has been sitting there for months... which means I've been twiddling my thumbs for months.
I figured a working unit test would be more helpful. Anyone can checkout the PR and they have a repro ready to go.

Bad-codegen bugs are really bad.

[TurkeyMan]

I was also interested to see the matrix of targets where this fails.
I thought it was only linux 64...

[WalterBright]

I see you added the bugzilla reference after I posted that, thank you. The Bugzilla should also be in the PR title, something like "Test case for Issue 19563 extern(C++) Incorrect ABI passing small struct"

[ghost]

#9295