fix TBB - clang feature detection problem symptoms
It looks like the feature detection of TBB does not recognize
that clang 5.0 with -std=c++14 supports variadic templates, and
thus (wrongly) disables tbb::concurrent_bounded_queue::emplace.
This commit fixes the symptom, and uses push instead of emplace.
Should be reverted once the underlying problem is fixed.
Edited by Gerhard Raven