Convert flatland to Android.bp

Due to the inability to use GoogleBenchmarkTest for testing, the
auto_gen_config is set to false. It is preferable for users to conduct
manual testing when needed.

Bug: 319579558
Test: 1. m flatland
      2. adb push flatland64
      3. run flatland64
Change-Id: Id05beb868b9c7d6afcac237f36a60f83cd4ebcc0