Convert libandroid and libandroid_runtime to Android.bp

See build/soong/README.md for more information.

Test: m -j checkbuild
Change-Id: Ie3c9c3d3c8c75ade36422d1e8ee0a5fe117e9091
(cherry picked from commit 3f8fd40f285dba5b3639ee1e3d4e4544048c1446)
diff --git a/Android.bp b/Android.bp
index 4f2e6d0..4ab5f1f 100644
--- a/Android.bp
+++ b/Android.bp
@@ -51,6 +51,7 @@
 }
 
 subdirs = [
+    "core/jni",
     "libs/*",
     "tools/*",
     "native/android",