ONNX Runtime Addition, master branch (2020.03.02.)
This is to replace !583 (merged), which it is based on.
The MR adds a new package (Externals/onnxruntime) that builds the ONNX Runtime library/framework/toolkit using the source code picked up from GitHub.
The build of ONNX Runtime makes use of a number of "externals", which it just ships with its own source code. For a long time we were discussing this with @dbakshig and the developers at Microsoft, and finally the conclusion is that it should be safe for us. (Hopefully...) The shared library created by the build (libonnxruntime.so) hides all of its symbols beside the public API that it provides. So the fact that it uses a different version of Eigen internally than what the rest of the ATLAS code does, should not actually hurt us.
Also note that the current setup builds all of the unit tests of the code. Unfortunately switching this off (onnxruntime_BUILD_UNIT_TESTS=FALSE) makes the build fail.