Switch to blueprint's microfactory

Bug: 63720725
Test: m -j nothing
Test: mkdir o; ../bootstrap.bash; ./soong
Change-Id: Id1f8312678f36afd08b49f8511fec3e6e5ba8de2
diff --git a/cmd/soong_env/Android.bp b/cmd/soong_env/Android.bp
index b0d827c..4cdc396 100644
--- a/cmd/soong_env/Android.bp
+++ b/cmd/soong_env/Android.bp
@@ -20,5 +20,6 @@
     srcs: [
         "soong_env.go",
     ],
+    default: true,
 }