symlink derived data path in Xcode build phase

link_derived_folder.sh

# create a symlink to avoid the the ugly-long-hard-remember derived data path like:
# ~/Library/Developer/Xcode/DerivedData/XXXXXX-aeuhuddtlmcrpvczljaagufyzgpw/Build/Products/Debug/

if [ -L build ];then
  rm -rf build
fi

if [ ! -d build ]; then
    ln -s "${BUILT_PRODUCTS_DIR}" build
fi