message: Use `make distclean` instead of `make clean`
  This commit replaces `make clean` by `make distclean` in `generate_docs.sh`.
  Reason: `make distclean` deletes `build` directory which is what we want.
diff: @@ -23,8 +23,8 @@ install_prefix="$source_dir/install"
  if [ "$skip_checks" = false ]; then
  # Clean-up build & install directory
  - if [ -d $source_dir/build ] && [ "$(ls $source_dir/build/default)" ] || [ -d $install_prefix ] ; then
  - printf "Clean-up your build & install directory using below command.\nmake clean && rm -rf $install_prefix\n"
  + if [ -d $source_dir/build ] || [ -d $install_prefix ] ; then
  + printf "Clean-up your build & install directory using below command.\nmake distclean && rm -rf $install_prefix\n"
  exit 1
  fi
  fi
  