internal/dl: add linux/arm64 to the list of First Class ports

The PrimaryPort function is used in the dl page to split downloads
between first class and "Others". Since linux/arm64 is now a first
class port, it needs to be listed in the primary section.

Updates golang/go#35593
Fixes golang/go#38258

Change-Id: Ib3044b2feaad4b7b415d273fab014d83082c806f
Run-TryBot: Alberto Donizetti <>
TryBot-Result: Gobot Gobot <>
Reviewed-by: Dmitri Shuralyov <>
diff --git a/internal/dl/dl.go b/internal/dl/dl.go
index e746fd1..9d83300 100644
--- a/internal/dl/dl.go
+++ b/internal/dl/dl.go
@@ -94,6 +94,7 @@
 	"linux/386":     true,
 	"linux/amd64":   true,
 	"linux/armv6l":  true,
+	"linux/arm64":   true,
 	"windows/386":   true,
 	"windows/amd64": true,