[clang] [C++20] [Modules] [Itanium ABI] Generate the vtable in the module unit of dynamic classes (PR #75912)

[Chuanqi Xu via cfe-commits]

ChuanqiXu9 wrote:

> FYI, the commit [99873b3](https://github.com/llvm/llvm-project/commit/99873b35da7ecb905143c8a6b8deca4d4416f1a9), which lists this PR as a motivator, causes breakage building a project, which I am still looking for a reduced test case.
> 
> The commit is not NFC despite what is says, just by cursory inspection of the change.
> 
> Please avoid adding NFC tag to such commits in the future and create a pull request.

Oh, sorry, I took another look at the commit and it looks the change makes it not a NFC change is this line: https://github.com/llvm/llvm-project/commit/99873b35da7ecb905143c8a6b8deca4d4416f1a9#diff-6fe53759e8d797c328c73ada5f3324c6248a8634ef36131c7eb2b9d89192bb64R6514

This shouldn't be in that commit but in this commit. It is not intentional. I guess we can't observe that if we put that in this PR too. And that change looks not bad. So maybe it makes something already bad to show up. 

https://github.com/llvm/llvm-project/pull/75912