The `GORISCV64` environment variable defaults to `rva20u64`.

### Wasm {#wasm}

<!-- go.dev/issue/63718 -->
The `go_wasip1_wasm_exec` script in `GOROOT/misc/wasm` has dropped support

	  ppc64.power8, ppc64.power9, and ppc64.power10
	  (or ppc64le.power8, ppc64le.power9, and ppc64le.power10)
	  feature build tags.
	- For GOARCH=riscv64,
	  GORISCV64=rva20u64 and rva22u64 correspond to the riscv64.rva20u64
	  and riscv64.rva22u64 build tags.
	- For GOARCH=wasm, GOWASM=satconv and signext
	  correspond to the wasm.satconv and wasm.signext feature build tags.

//     (or ppc64le.power8, ppc64le.power9, and ppc64le.power10)
//     feature build tags.
//   - For GOARCH=riscv64,
//     GORISCV64=rva20u64 and rva22u64 correspond to the riscv64.rva20u64
//     and riscv64.rva22u64 build tags.
//   - For GOARCH=wasm, GOWASM=satconv and signext
//     correspond to the wasm.satconv and wasm.signext feature build tags.
//

	if b == "" {
		b = "hardfloat"
	}
	gomips64 = b

	b = os.Getenv("GOPPC64")
	if b == "" {
		b = "power8"
	}
	goppc64 = b

	b = os.Getenv("GORISCV64")
	if b == "" {
		b = "rva20u64"
	}
	goriscv64 = b

	if p := pathf("%s/src/all.bash", goroot); !isfile(p) {
		fatalf("$GOROOT is not set correctly or not exported\n"+
			"\tGOROOT=%s\n"+
			"\t%s does not exist", goroot, p)
	}