Regression in benchmark_material with clang

[romeric]

There is a slight regression while compiling benchmark_material with apple clang on macOS. seems to be related to changes permutation. The regression was introduced with this commit apparently 97179bb. GCC is unaffected.

Nothing seems suspicious but requires further testing and verifications.

[romeric]

The issue was that generic version of permutation was being used due to a bug in the return type of tensor permutation that made it never get activated. Fix now [aace93e
]