Migrate liblog to ndk_library.

Test: make native
Bug: http://b/30465923
Change-Id: I3db7ede817a57b3505c0556ea28f08b9e8331e1a
diff --git a/liblog/Android.bp b/liblog/Android.bp
index e32f73c..ba7cc8a 100644
--- a/liblog/Android.bp
+++ b/liblog/Android.bp
@@ -91,3 +91,9 @@
     compile_multilib: "both",
     stl: "none",
 }
+
+ndk_library {
+    name: "liblog.ndk",
+    symbol_file: "liblog.map.txt",
+    first_version: "9",
+}