title: lib.so missing and no known rule to make it
body: <p>From google examples I'm trying to customize hello-libs example addind my shared library libofr_engine_core</p>
  
  <p>but i receive this error...</p>
  
  <p>Error:error: 'C:/Users/.../Downloads/android-ndk-master/hello-libs/distribution/ofr/lib/arm64-v8a/libofr_engine_core.so', needed by 'C:/Users/.../Downloads/android-ndk-master/hello-libs/app/build/intermediates/cmake/debug/obj/arm64-v8a/libhello-libs.so', missing and no known rule to make it</p>
  
  <p>What I'm doing wrong?</p>
  
  <p>Obviously I have added the .so and .h to my distribution folder</p>
  
  <pre><code>cmake_minimum_required(VERSION 3.4.1)
  
  # configure import libs
  set(distribution_DIR ${CMAKE_SOURCE_DIR}/../../../../distribution)
  
  add_library(lib_gmath STATIC IMPORTED)
  set_target_properties(lib_gmath PROPERTIES IMPORTED_LOCATION
      ${distribution_DIR}/gmath/lib/${ANDROID_ABI}/libgmath.a)
  
  # shared lib will also be tucked into APK and sent to target
  # refer to app/build.gradle, jniLibs section for that purpose.
  # ${ANDROID_ABI} is handy for our purpose here. Probably this ${ANDROID_ABI} is
  # the most valuable thing of this sample, the rest are pretty much normal cmake
  add_library(lib_gperf SHARED IMPORTED)
  set_target_properties(lib_gperf PROPERTIES IMPORTED_LOCATION
      ${distribution_DIR}/gperf/lib/${ANDROID_ABI}/libgperf.so)
  
  
  add_library(libofr_engine_core SHARED IMPORTED)
  set_target_properties(libofr_engine_core PROPERTIES IMPORTED_LOCATION
      ${distribution_DIR}/ofr/lib/${ANDROID_ABI}/libofr_engine_core.so)
  
  
  
  # build application's shared lib
  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=gnu++11")
  
  add_library(hello-libs SHARED
              hello-libs.cpp)
  
  target_include_directories(hello-libs PRIVATE
                             ${distribution_DIR}/gmath/include
                             ${distribution_DIR}/gperf/include
                             ${distribution_DIR}/ofr/include
                             )
  
  target_link_libraries(hello-libs
                        android
                        lib_gmath
                        lib_gperf
                        libofr_engine_core
                        log)
  </code></pre>