Add libarena from local rust to stage0
This was needed at least when local rust was 1.9.0 on darwin.
Fixes #35149
cp ${PREFIX}/bin/rustc${BIN_SUF} ${TARG_DIR}/stage0/bin/
cp ${PREFIX}/${LIB_DIR}/${RUSTLIBDIR}/${TARG_DIR}/${LIB_DIR}/* ${TARG_DIR}/stage0/${LIB_DIR}/
+cp ${PREFIX}/${LIB_DIR}/${LIB_PREFIX}arena*${LIB_SUF} ${TARG_DIR}/stage0/${LIB_DIR}/
cp ${PREFIX}/${LIB_DIR}/${LIB_PREFIX}extra*${LIB_SUF} ${TARG_DIR}/stage0/${LIB_DIR}/
cp ${PREFIX}/${LIB_DIR}/${LIB_PREFIX}rust*${LIB_SUF} ${TARG_DIR}/stage0/${LIB_DIR}/
cp ${PREFIX}/${LIB_DIR}/${LIB_PREFIX}std*${LIB_SUF} ${TARG_DIR}/stage0/${LIB_DIR}/