Enable --android-platform-build for libcore projects

This is to turn-off d8 desugaring in libcore itself.

Bug: 232073181
Test: atest CtsLibcoreTestOjCases CtsLibcoreTestCases
Change-Id: I534eb6d78da8900b68152073ca9e4a4b91508ad9
diff --git a/JavaLibrary.bp b/JavaLibrary.bp
index d0558d1..bed3a0a 100644
--- a/JavaLibrary.bp
+++ b/JavaLibrary.bp
@@ -153,7 +153,10 @@
         //"-Xlint:all",
         //"-Xlint:-serial,-deprecation,-unchecked",
     ],
-    dxflags: ["--core-library"],
+    dxflags: [
+        "--android-platform-build",
+        "--core-library",
+    ],
     errorprone: {
         javacflags: [
             "-Xep:MissingOverride:OFF", // Ignore missing @Override.