cmd/dist, go/types: add support for GOARCH=riscv64

This is needed in addition to CL 110066 in order to be able to generate
Go type definitions for linux/riscv64 in the golang.org/x/sys/unix
package.

Change-Id: I4a27e6424aaea63283b55bd4f73b958b41f29d72
Reviewed-on: https://go-review.googlesource.com/118618
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/dist/build.go

@@ -67,6 +67,7 @@ var okgoarch = []string{
 	"mips64le",
 	"ppc64",
 	"ppc64le",
+	"riscv64",
 	"s390x",
 	"wasm",
 }
@@ -1393,6 +1394,7 @@ var cgoEnabled = map[string]bool{
 	"linux/mipsle":    true,
 	"linux/mips64":    true,
 	"linux/mips64le":  true,
+	"linux/riscv64":   true,
 	"linux/s390x":     true,
 	"android/386":     true,
 	"android/amd64":   true,

src/cmd/vet/all/main.go

@@ -197,6 +197,11 @@ func (p platform) vet() {
 		fmt.Println("skipping js/wasm")
 		return
 	}
+	if p.os == "linux" && p.arch == "riscv64" {
+		// TODO(tklauser): enable as soon as the riscv64 port has fully landed
+		fmt.Println("skipping linux/riscv64")
+		return
+	}
 
 	var buf bytes.Buffer
 	fmt.Fprintf(&buf, "go run main.go -p %s\n", p)

src/go/types/sizes.go

@@ -167,6 +167,7 @@ var gcArchSizes = map[string]*StdSizes{
 	"mips64le": {8, 8},
 	"ppc64":    {8, 8},
 	"ppc64le":  {8, 8},
+	"riscv64":  {8, 8},
 	"s390x":    {8, 8},
 	"wasm":     {8, 8},
 	// When adding more architectures here,
@@ -178,7 +179,7 @@ var gcArchSizes = map[string]*StdSizes{
 //
 // Supported architectures for compiler "gc":
 // "386", "arm", "arm64", "amd64", "amd64p32", "mips", "mipsle",
-// "mips64", "mips64le", "ppc64", "ppc64le", "s390x", "wasm".
+// "mips64", "mips64le", "ppc64", "ppc64le", "riscv64", "s390x", "wasm".
 func SizesFor(compiler, arch string) Sizes {
 	if compiler != "gc" {
 		return nil