unroll loop for icc

This was the change I needed to make to the source to get the CPU platform to compile with icc in #202. I'm not sure that it's worth merging, especially since `icc` seems so slow, but without it, you get the compilation error `catastrophic error: Intrinsic parameter must be an immediate value`. I tried using icc flags for aggressive loop unrolling, figuring that they should (?) unroll that loop over `j` which should (?) solve the problem, but I still got the compilation error.