check libnccl instead of nccl to be more reliable

[dengl11]

grep nccl may not be a reliable way to check if nccl is installed;

for example, on my workstation:

$ dpkg -l | grep nccl

shows

ii  libvncclient1:amd64                        0.9.13+dfsg-3build2                     amd64        API to write one's own VNC server - client library
ii  nccl-local-repo-ubuntu2204-2.22.3-cuda12.2 1.0-1                                   amd64        nccl-local repository configuration files

and the Makefile mistakenly thinks that I have nccl installed, and then tries to link nccl, and then failed.

So changing it to grep libnccl to be slightly more reliable; I installed nccl, and then verified that

dpkg -l | grep libnccl

shows

ii  libnccl2                                   2.22.3-1+cuda12.2                       amd64        NVIDIA Collective Communication Library (NCCL) Runtime