what about the mac-os(or linux,etc) native libraries on windows where you're building the demo code? The 60MB zig compiler and native clang on Windows will not have them, how is that done? Is it totally on clang side?
At work we could not for that reason use the same compilation server setup to cross-compile for Linux, MacOS, Windows and ended up with a separated MacPro box for the compilation farm.
EDIT: cross-compilation from Windows works after one gets Windows SDK and Visual Studio libraries (the later is not free, but free alternatives often are sufficient). The biggest headache is that Windows headers assume a case-insensitive file system and includes, for example, windows.h when the file is Windows.h. One can either use case-insensitive mount option for ext4 or symlink relevant files to the proper case.
Another Clang-specific way to handle the case insensitivity is by making use of a virtual file system (VFS) overlay. https://github.com/llvm/llvm-project/blob/4976d1fe58f89169ef... demonstrates how that works. (There's no linker equivalent that I'm aware of, so you do have to use the symlinks or something like ciopfs for that; https://github.com/llvm/llvm-project/blob/4976d1fe58f89169ef... is an example of symlink generation.)
If you need the rest of the Apple SDK, then you'd need a sysroot (and face the challenges you described.)