While Rust doesn't have C coverage, it has (by my last check) better coverage than something like CPython currently does.
The big thing though is Rust is honest about their tiers of support, whereas for many projects "supported platform" for minor platforms often mean "it still compiles (at least we think it does, when the maintainer tries it and it fails they will fix it)"
Not to be too glib though, there are obviously tools out there that have as much or more rigor than Rust and cover more platforms. Just... "supported platforms" means different things in different contexts.
All too common (not just with compilers) for someone to port the subset they care about and declare it done. Rust's decision to create standards of compliance and be conscious about which platforms are viable targets and which ones don't meet their needs is a completely valid way to ensure that whole classes of trouble never come. I think it's a completely valid approach, despite complaints from some.
The big thing though is Rust is honest about their tiers of support, whereas for many projects "supported platform" for minor platforms often mean "it still compiles (at least we think it does, when the maintainer tries it and it fails they will fix it)"
Not to be too glib though, there are obviously tools out there that have as much or more rigor than Rust and cover more platforms. Just... "supported platforms" means different things in different contexts.