Cross compiling to macOS is broken on non macOS hosts

[yorickpeterse]

Please describe the bug

Starting with 0.16.0, macOS builds link against the "Security" and "CoreFoundation" frameworks. When cross compiling from a non macOS host to macOS, these frameworks aren't available due to the macOS SDK not being readily available. Using Zig as the linker won't work either, because it doesn't provide a full SDK that's needed for this.

Since we can't ship the SDK (even if we could, it's massive), we need to document how to handle this.

Related:

• Cross-compilation from LInux to x86_64-apple-darwin fails due to bad "cc" command line params rust-lang/rust#112501
• ability to link against darwin frameworks (such as CoreFoundation) when cross compiling ziglang/zig#1349
• https://github.com/roblabla/MacOSX-SDKs/tree/master
  • https://developer.apple.com/forums/thread/114179

Operating system

Fedora

Inko version

0.16.0