Use -target 8 for core-lambda-stubs

core-lambda-stubs is distributed as part of the SDK and should use
-target 8 for compatibility with old JDKs.

Bug: 150153790
Bug: 162522383
Test: javap -v --system none -bootclasspath "" -cp out/target/common/obj/JAVA_LIBRARIES/core-lambda-stubs_intermediates/classes.jar java.lang.invoke.LambdaMetafactory | grep "major version"
Change-Id: I73fcfefb353099fa6545b2ff1d2b2fcf677931ae
Merged-In: I73fcfefb353099fa6545b2ff1d2b2fcf677931ae
(cherry picked from commit dafdf70fc4c8cc8853aa04ece2f59db864550618)
diff --git a/JavaLibrary.bp b/JavaLibrary.bp
index 0d98122..8b0ab3b 100644
--- a/JavaLibrary.bp
+++ b/JavaLibrary.bp
@@ -406,6 +406,9 @@
         ":openjdk_lambda_stub_files",
         ":openjdk_lambda_duplicate_stub_files",
     ],
+    // This jar is packaged as part of the SDK, use -target 8 so that it works
+    // with old JDKs.
+    java_version: "1.8",
 }
 
 // An alternative to core-lambda-stubs that omits openjdk_lambda_duplicate_stub_files