Fail XCCL build when oneCCL is missing instead of warning#2380

pkourdis wants to merge 2 commits intometa-pytorch:mainmeta-pytorch/torchcomms:mainfrom

pkourdis:xccl-fatal-on-missing-onecclpkourdis/torchcomms:xccl-fatal-on-missing-onecclCopy head branch name to clipboard