What language, between Go and Rust, would you use to create a library for games (no bindings)?
Go is a simpler language that leans more heavily on garbage collection. Rust is a more complex language that can be safely used without the GC at all which is perfect for low-level systems programming.
I'm biased since I spent two summers working on Rust, but if you're willing to invest the necessary time to keep up with a rapidly changing language, Rust would be really good for games. It has a really nice set of built in concurrency primitives, so it would be easy to separate the different components such as the rendering engine, the AI, etc. and take advantage of multicore computers. It's also possible to avoid the need for garbage collection, so you don't have to worry about unpredictable GC pauses. It's designed to integrate nicely with existing C code, and many of the data types map directly onto C types. Rust's approach to polymorphism leads to some really nice assembly once LLVM is done with it.
Many games nowadays are running in the web browser, which suggests that web browsers and games have similar requirements. Mozilla is designing Rust alongside its new parallel browser engine, which means the language will continue to evolve in ways that would work well for game programming too.
Rust: This is alpha-level software with many known bugs, incomplete features and planned future changes. Use at your own risk, expect some instability, disruption and source-level incompatibility for a while yet. No good for commercial game.
You can't make library with Go for games at all. There is no support to create library in Go. With Go you can create mobule(library) that you will use only with Go.
You can use C++ library in Go. But you can't use Go lib in C++.
You may ask what language is better for games Rust or Go.
UPDATE 2015 year Go 1.4 has office/beta support for Android and Go 1.5 (2015 Summer) will have iOS support.
Right now it is tricky to build for android. You have to install docker image