Some people talk about 68k not being supported being a problem
Rust also has an experimental GCC-based codegen backend (based on libgccjit (which isn't used as a JIT)).
So platforms that don't have either LLVM nor recent GCC are screwed.
additionally, I believe the GCC backend is incomplete. the `core` library is able to compile, but rust's `std` cannot be.
Not having a recent GCC and not having GCC are different things. There may be architectures that have older GCC versions, but are no longer supported for more current C specs like C11, C23, etc.