dashboard: reenable linux-amd64-alpine

It passes all.bash in the main repo after CL 419995.

For golang/go#19938.

Change-Id: I03c32193bbc83667e7bbbb2251e15a4a9bef6cfc
Reviewed-on: https://go-review.googlesource.com/c/build/+/420214
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Carlos Amedee <carlos@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>

dashboard/builders.go

@@ -1591,14 +1591,10 @@ func init() {
 		HostType:   "host-linux-amd64-stretch-vmx",
 		buildsRepo: disabledBuilder,
 	})
-
-	const testAlpine = false // Issue 22689 (hide all red builders), Issue 19938 (get Alpine passing)
-	if testAlpine {
-		addBuilder(BuildConfig{
-			Name:     "linux-amd64-alpine",
-			HostType: "host-linux-amd64-alpine",
-		})
-	}
+	addBuilder(BuildConfig{
+		Name:     "linux-amd64-alpine",
+		HostType: "host-linux-amd64-alpine",
+	})
 
 	// addMiscCompileGo1 adds a misc-compile TryBot that
 	// runs buildall.bash on the specified target(s), up to 3 max.

dashboard/builders_test.go

@@ -669,9 +669,7 @@ func TestBuilderConfig(t *testing.T) {
 }
 
 func TestHostConfigsAllUsed(t *testing.T) {
-	knownUnused := map[string]bool{
-		"host-linux-amd64-alpine": true, // TODO(golang.org/issue/19938): Fix the Alpine builder, or remove it.
-	}
+	knownUnused := map[string]bool{}
 
 	used := make(map[string]bool)
 	for _, conf := range Builders {