/usr/alpha-linux-gnu/lib/libobjc.so.4 is in libobjc4-alpha-cross 6.3.0-18cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/alpha-linux-gnu/lib/libobjc.so.4.0.0
/usr/alpha-linux-gnu/lib/libobjc.so.4.0.0