[clang] [clang] Mangle C++20 module ownership for the Microsoft ABI (PR #220820)

[Reid Kleckner via cfe-commits]

rnk wrote:

I should add, thanks for the fix, the tests actually look good, and I think the code isn't too complicated with some simplifications. 🙏 

https://github.com/llvm/llvm-project/pull/220820