dashboard: update Dragonfly tip policy for ABI change, add release builder

From https://github.com/golang/go/issues/34958#issuecomment-543852995 :

> Go's DragonFly support policy is that we support the latest stable
> release primarily, but also try to keep DragonFly master passing, in
> prep for it to become the latest stable release.
>
> But that does mean we need one more builder at the moment.

Updates golang/go#34958
Updates golang/go#23060

Change-Id: I84be7c64eac593dee2252c397f9529deea13605a
Reviewed-on: https://go-review.googlesource.com/c/build/+/202478
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
diff --git a/dashboard/builders_test.go b/dashboard/builders_test.go
index e7a7699..51f4f5f 100644
--- a/dashboard/builders_test.go
+++ b/dashboard/builders_test.go
@@ -524,6 +524,14 @@
 		// that'll never be fixed.
 		{b("freebsd-386-11_2@go1.11", "net"), none},
 		{b("freebsd-386-12_0@go1.11", "net"), none},
+
+		{b("dragonfly-amd64", "go"), onlyPost},
+		{b("dragonfly-amd64", "net"), onlyPost},
+		{b("dragonfly-amd64@go1.13", "net"), none}, // Dragonfly ABI changes only supported by Go 1.14+
+		{b("dragonfly-amd64@go1.13", "go"), none},  // Dragonfly ABI changes only supported by Go 1.14+
+		{b("dragonfly-amd64-5_6", "go"), onlyPost},
+		{b("dragonfly-amd64-5_6", "net"), onlyPost},
+		{b("dragonfly-amd64-5_6@go1.13", "net"), onlyPost},
 	}
 	for _, tt := range tests {
 		t.Run(tt.br.testName, func(t *testing.T) {