message: build using 4 cpus on docker container, cleanup
diff: # ../build/libs/${LIBRARY_NAME}-android-arm-<version>.jar
  # remote android-arm build with travis is available at https://s3.amazonaws.com/gubatron-jlibtorrent/release/android/arm64-v8a/libjlibtorrent.so
  source build-utils.shinc
  -check_min_req_vars
  export os_arch=arm
  export os_build=android
  export android_api=21
  export SHARED_LIB=lib${LIBRARY_NAME}.so
  -export CXX=g++
  +#export CXX=g++
  export NDK_VERSION=r21d
  -prepare_android_toolchain
  -abort_if_var_unset "ANDROID_TOOLCHAIN" ${ANDROID_TOOLCHAIN}
  +export ANDROID_TOOLCHAIN="/src/android-toolchain-arm"
  +
  +#export CXX=${ANDROID_TOOLCHAIN}/bin/arm-linux-androideabi-clang++
  +export CXX=${ANDROID_TOOLCHAIN}/bin/armv7a-linux-androideabi${android_api}-clang++
  export CC=${ANDROID_TOOLCHAIN}/bin/armv7a-linux-androideabi${android_api}-clang
  -export run_openssl_configure="./Configure linux-${os_arch}v4 ${OPENSSL_NO_OPTS} -march=armv7-a -mfpu=neon -fPIC --prefix=${OPENSSL_ROOT}";
  +
  +android_env
  +common_env
  +check_min_req_vars
  +
  export run_readelf="${ANDROID_TOOLCHAIN}/bin/arm-linux-androideabi-readelf -d bin/release/${os_build}/${os_arch}eabi-v7a/${SHARED_LIB}"
  -export run_bjam="${BOOST_ROOT}/b2 -j8 --user-config=config/${os_build}-${os_arch}-config.jam variant=release toolset=clang-linux-${os_arch} target-os=${os_build} location=bin/release/${os_build}/${os_arch}eabi-v7a"
  +export run_bjam="${BOOST_ROOT}/b2 -j4 --user-config=config/${os_build}-${os_arch}-config.jam variant=release toolset=clang-linux-${os_arch} target-os=${os_build} location=bin/release/${os_build}/${os_arch}eabi-v7a"
  export run_strip="${ANDROID_TOOLCHAIN}/bin/arm-linux-androideabi-strip --strip-unneeded -x -g bin/release/${os_build}/${os_arch}eabi-v7a/${SHARED_LIB}"
  export run_objcopy="${ANDROID_TOOLCHAIN}/bin/arm-linux-androideabi-objcopy --only-keep-debug bin/release/${os_build}/${os_arch}eabi-v7a/${SHARED_LIB} bin/release/${os_build}/${os_arch}eabi-v7a/${SHARED_LIB}.debug"
  -export PATH=$ANDROID_TOOLCHAIN/arm-linux-androideabi/bin:$PATH;
  +export PATH=${ANDROID_TOOLCHAIN}/arm-linux-androideabi/bin:$PATH;
  sed -i 's/RANLIB = ranlib/RANLIB = "${ANDROID_TOOLCHAIN}\/bin\/arm-linux-androideabi-ranlib"/g' ${BOOST_ROOT}/tools/build/src/tools/gcc.jam;
  create_folder_if_it_doesnt_exist ${SRC}
  prompt_msg "About to prepare BOOST ${BOOST_VERSION}"
  press_any_to_continue
  -prepare_boost
  -prepare_openssl
  -build_openssl
  -prepare_android_standalone_toolchain
  -export CC=${ANDROID_TOOLCHAIN}/bin/armv7a-linux-androideabi${android_api}-clang++
  prepare_libtorrent
  ./run-swig.sh
  build_libraries
  