message: Check build dir first (generate_docs.sh)
  To start with there will be no build directory. But after building once, `build/default` get generated.
  When we issue `make clean`, `build/default` still exists; but empty.
  Also, `$install_prefix` represents a directory, so added `-d` instead of `-e`.
diff: @@ -23,7 +23,7 @@ install_prefix="$source_dir/install"
  if [ "$skip_checks" = false ]; then
  # Clean-up build & install directory
  - if [ "$(ls $source_dir/build/default)" ] || [ -e $install_prefix ] ; then
  + 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"
  exit 1
  fi
  