Dear @jdad: I implemented your changes in the dy/powerpc branch and opened a pull request: https://github.com/denizyuret/Knet.jl/pull/625
I confirmed that -std=c++11 option did not break x86_64 and copied your precompiled tar.gz to the main Knet repo. Please confirm that this branch works for you and I will merge it to master.
Thanks!