Alter build.gradle

build.gradle

android {
  // ...
  defaultConfig {
    // ...
    // the following configures ndk-build to build a "helloworld" module
    ndk {
      abiFilters "armeabi-v7a", "x86"
      moduleName "helloworld"
      ldLibs "log"
    }
  } 
  // ...
  // Here we can add source code to our project
  sourceSets {
    main {
      // first our new Java code
      java.srcDirs = ["../../djinni/java", "src/main/java"]
      // second our JNI classes
      jni.srcDirs = ["../../djinni/jni"]
    }
  }
  externalNativeBuild {
    // This points ndk-build at our Android.mk file
    ndkBuild {
      path file('src/main/jni/Android.mk')
    }
  }
  //...
}