dashboard: don't build x/net master against Go 1.12 on aix

Per request in https://golang.org/issue/31564#issuecomment-484786144

Change-Id: I52e496083b84aa021e7d7cdcda19c96980e1518f
Reviewed-on: https://go-review.googlesource.com/c/build/+/172878
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
diff --git a/dashboard/builders.go b/dashboard/builders.go
index 0fc522b..694ed88 100644
--- a/dashboard/builders.go
+++ b/dashboard/builders.go
@@ -2137,6 +2137,15 @@
 		env: []string{
 			"PATH=/opt/freeware/bin:/usr/bin:/etc:/usr/sbin:/usr/ucb:/usr/bin/X11:/sbin:/usr/java7_64/jre/bin:/usr/java7_64/bin",
 		},
+		buildsRepo: func(repo, branch, goBranch string) bool {
+			switch repo {
+			case "net":
+				// The x/net package wasn't working in Go 1.12; AIX folk plan to have
+				// it ready by Go 1.13. See https://golang.org/issue/31564#issuecomment-484786144
+				return atLeastGo1(branch, 13) && atLeastGo1(goBranch, 13)
+			}
+			return atLeastGo1(branch, 12) && atLeastGo1(goBranch, 12)
+		},
 	})
 
 }
diff --git a/dashboard/builders_test.go b/dashboard/builders_test.go
index 4131d40..4e7d673 100644
--- a/dashboard/builders_test.go
+++ b/dashboard/builders_test.go
@@ -338,7 +338,8 @@
 		{b("aix-ppc64", "go"), onlyPost},
 		{b("aix-ppc64", "net"), onlyPost},
 		{b("aix-ppc64@go1.12", "go"), onlyPost},
-		{b("aix-ppc64@go1.12", "net"), onlyPost},
+		{b("aix-ppc64@go1.12", "net"), none},
+		{b("aix-ppc64@go1.13", "net"), onlyPost},
 		{b("aix-ppc64@go1.11", "go"), none},
 		{b("aix-ppc64@go1.11", "net"), none},