I develop for Linux, Mac, and Windows. Multiple architectures and OSes. I rarely see platform issues with Rust. It's typically only stuff at the edge, like CUDA libraries, that trip up cross-platform builds.
Rust, as a systems language, is quite good at working on a variety of systems.
Starts already that Rust won't support architectures not available on LLVM, but on GCC, otherwise having a Rust frontend project for GCC wouldn't be a thing.
And the systems language remark, I am still looking forward when sorting ABI issues for binary libraries is finally something that doesn't need to go through solutions designed for C and C++.
Rust, as a systems language, is quite good at working on a variety of systems.