I am using sh-elf-gccgo (GCC) 15.1.0 which is ok-ish I guess. But in general gccgo tries to be close to Go, but they do not implement all the features. e.g. generics are still missing for example.
problem is TinyGo uses LLVM, which doesn't support SH-4. The only reason I went with gccgo is due to SH4 target. In any case, I learned a ton of things doing this project :D