Function can_be_bundled 

pub fn can_be_bundled(target: TargetTuple) -> bool

Whether we can produce a sysroot for this target without the user fetching anything.

Section 8.2’s table has seven rows and two of them are legal walls rather than engineering. The macOS SDK is restricted by the Xcode licence to Apple-branded hardware and the Windows SDK is not redistributable, so for those two the answer is a path the user supplies under their own licence, and spec/cross-compile/13-distribution.md owns the mechanism.

This returns false for those two and true for everything else, including freestanding, which needs nine compiler headers and no link inputs at all.