Build Go tools for arm

Test: prebuilts/build-tools/build-prebuilts.sh
Change-Id: I915be7bb7451f27fcd4beba5e6487da7a01639a6
diff --git a/scripts/microfactory.bash b/scripts/microfactory.bash
index ce4a0e4..49988fa 100644
--- a/scripts/microfactory.bash
+++ b/scripts/microfactory.bash
@@ -23,7 +23,14 @@
 # Ensure GOROOT is set to the in-tree version.
 case $(uname) in
     Linux)
-        export GOROOT="${TOP}/prebuilts/go/linux-x86/"
+        case $(uname -m) in
+            x86_64)
+                export GOROOT="${TOP}/prebuilts/go/linux-x86/"
+                ;;
+            aarch64)
+                export GOROOT="${TOP}/prebuilts/go/linux-arm64/"
+                ;;
+        esac
         ;;
     Darwin)
         export GOROOT="${TOP}/prebuilts/go/darwin-x86/"