That's not the base language, it's an unsafe superset. There's no reason why a Wasm-GC backend for Golang should be expected to support that by default.
If it is part of the language reference it is part of the language.
Usually when language reference books used to be printed, or we used ISO languages, what is there on paper, is the language.
We are only discussing semantics, if it is hardcoded primitives, or made available via the standard library, specially in case of blessed packages like unsafe which aren't fully implemented, rather magical types for the compiler.
Which is nothing new since the 1960's that there are systems languages with some way to mark code unsafe, the C linage of languages are the ones that decided to ignore this approach.
The standard library uses unsafe for syscalls, for higher-performance primitives like strings.Builder, etc, so it's support is mandatory to run any non-trivial Go program
For a while the GOOS=nacl port and the Google App Engine ports of Go disallowed unsafe pointer manipulation too, so there is some precedent. Throughout some of the ecosystem you can see pieces of "nounsafe" build tag support (e.g. in easyjson).
Most programming languages that offer unsafe, either as language keyword, or meta package (unsafe/SYSTEM/UNSAFE whatever the name), have similar option, that doesn't make it less of a feature.
Somehow I don't think Wasm-GC is going to support bare metal syscalls anytime soon. That stuff all has to be rewritten anyway if you want to target WASM.
It's not just system calls. E.g. reflection package uses unsafe too: https://github.com/golang/go/blob/master/src/reflect/value.g... .
Many packages from Go standard library use unsafe one way or the other, so it's not fair to say that unsafe package is separate from the rest of the language
