dashboard: add windows-arm64-10 reverse buildlet

This adds a reverse buildlet for Windows ARM64 running under qemu on M1
Mac Minis. The VM currently boots, but more changes are needed to
stage0 and buildlet in order for the builder to run.

For golang/go#42604.

Change-Id: Ie86e596c0f166d2ca8c075c0c971fcd1e34e940f
Reviewed-on: https://go-review.googlesource.com/c/build/+/328311
Trust: Alexander Rakoczy <alex@golang.org>
Run-TryBot: Alexander Rakoczy <alex@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>

dashboard/builders.go

@@ -476,6 +476,13 @@ var Hosts = map[string]*HostConfig{
 		isEC2:              true,
 		machineType:        "a1.metal",
 	},
+	"host-windows-arm64-mini": &HostConfig{
+		Notes:              "macOS hosting Windows 10 in qemu with HVM acceleration.",
+		buildletURLTmpl:    "http://storage.googleapis.com/$BUCKET/buildlet.windows-arm64",
+		env:                []string{"GOARCH=arm64"},
+		goBootstrapURLTmpl: "https://storage.googleapis.com/$BUCKET/gobootstrap-windows-arm64-f22ec5.tar.gz",
+		IsReverse:          true,
+	},
 	"host-darwin-10_12": &HostConfig{
 		IsReverse: true,
 		ExpectNum: 3,
@@ -2287,6 +2294,15 @@ func init() {
 		},
 		KnownIssue: 42604,
 	})
+	addBuilder(BuildConfig{
+		Name:              "windows-arm64-10",
+		HostType:          "host-windows-arm64-mini",
+		numTryTestHelpers: 1,
+		buildsRepo: func(repo, branch, goBranch string) bool {
+			return atLeastGo1(goBranch, 17) && buildRepoByDefault(repo)
+		},
+		KnownIssue: 42604,
+	})
 	addBuilder(BuildConfig{
 		Name:           "darwin-amd64-10_12",
 		HostType:       "host-darwin-10_12",