Add java sdk library enforcement flag

Add java sdk library enforcement for inter-partition library
dependency, for ensuring backward-compatible libraries for
inter-partition dependencies.

Test: m nothing
Bug: 168180538
Change-Id: I6bfac54c3499b03003a3bc6c2bb62b165b4ce5f9
diff --git a/java/Android.bp b/java/Android.bp
index 9e8dc78..39502b3 100644
--- a/java/Android.bp
+++ b/java/Android.bp
@@ -48,6 +48,7 @@
         "robolectric.go",
         "sdk.go",
         "sdk_library.go",
+        "sdk_library_external.go",
         "support_libraries.go",
         "sysprop.go",
         "system_modules.go",