/usr/lib/x86_64-linux-gnu/libclFFT.so is in libclfft-dev 2.10.2-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libclFFT.so.2
/usr/lib/x86_64-linux-gnu/libclFFT.so.2