Rust

What I'm getting at is that your fork can literally rip out the code that does floating point math. Rust's actual standard library won't do that, but it will probably some day take that cfg() parameter to turn off floating point math or agree some other way forward. Meanwhile Rust for Linux gets a library it can ship in Linux.

It's future proofed in that the assumption is some day Rust will have a way to disable or sidestep this, and at that point Rust for Linux can just ship the normal core library (in this respect).

The fact Rust's standard library relies on Rust's nightly features is orthogonal, this configuration parameter isn't relying on yet-to-stabilise feature, it's just that the code in core wants to do floating point maths, and Linux doesn't want that to be a possibility. In that specific case just ripping out the offending code is an effective solution, you could do it once for each Linux release and while somewhat tiresome it's not unmanageable.