Nice! Please note that there are updated patches in MSYS2-packages/llvm which replace some of the 'hack' patches with more proper methods (which I opened PRs upstream for, but I've not gotten any replies to them yet). Also, there is an issue currently outstanding, for which I opened an upstream PR but I'm waiting for feedback on if that was the proper way to fix it or not. (https://github.com/llvm/llvm-project/pull/136599).
I've also seen a crash with a simple "Hello world" C++ iostreams program, only on Cygwin not MSYS2. I suspect it is related to the C++11 ABI thing, but it is not worked around by defining the macro. There should also be a big red warning that, due to the macro being defined, clang++ and g++ compiled objects might not be able to link to each other if they try to pass std::strings (or possibly other stl objects) between them.
