/usr/lib/gcc-cross/alpha-linux-gnu/8/libobjc.so is in libobjc-8-dev-alpha-cross 8-20180414-1ubuntu2cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/gcc-cross/alpha-linux-gnu/8/../../../../alpha-linux-gnu/lib/libobjc.so.4