cmd/dist: add support for GOARCH=arm64

Change-Id: I92b4301b64054272d78dd15c16bf6ff592acad26
Reviewed-on: https://go-review.googlesource.com/7141Reviewed-by: Minux Ma <minux@golang.org>
Reviewed-by: Dave Cheney <dave@cheney.net>
Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/dist/build.go

@@ -49,7 +49,7 @@ var (
 )
 
 // The known architecture letters.
-var gochars = "566899"
+var gochars = "5667899"
 
 // The known architectures.
 var okgoarch = []string{
@@ -57,6 +57,7 @@ var okgoarch = []string{
 	"arm",
 	"amd64",
 	"amd64p32",
+	"arm64",
 	"386",
 	"ppc64",
 	"ppc64le",
@@ -909,6 +910,8 @@ var cleantab = []string{
 	"cmd/5l",
 	"cmd/6g",
 	"cmd/6l",
+	"cmd/7g",
+	"cmd/7l",
 	"cmd/8g",
 	"cmd/8l",
 	"cmd/9g",

src/cmd/dist/buildtool.go

@@ -27,6 +27,8 @@ var bootstrapDirs = []string{
 	"5l",
 	"6g",
 	"6l",
+	"7g",
+	"7l",
 	"8g",
 	"8l",
 	"9g",
@@ -41,6 +43,7 @@ var bootstrapDirs = []string{
 	"internal/ld",
 	"internal/obj",
 	"internal/obj/arm",
+	"internal/obj/arm64",
 	"internal/obj/ppc64",
 	"internal/obj/x86",
 	"old5a",

src/cmd/dist/util.go

@@ -422,6 +422,8 @@ func main() {
 			gohostarch = "386"
 		case strings.Contains(out, "arm"):
 			gohostarch = "arm"
+		case strings.Contains(out, "aarch64"):
+			gohostarch = "arm64"
 		case strings.Contains(out, "ppc64le"):
 			gohostarch = "ppc64le"
 		case strings.Contains(out, "ppc64"):