The model itself doesn't contain C++ code. The runtime supports Python, JS, etc. I don't think they are shipping a copy of clang as part of the rt. I could be wrong, I haven't looked. Of course it needs the scaffolding to get data in and out.
I just did an install of the runtime on Python ( pip install onnxruntime ) . Here are the additional packages it installs.
Package Version
------------- -------
coloredlogs 15.0.1
flatbuffers 23.5.26
humanfriendly 10.0
mpmath 1.3.0
numpy 1.25.2
onnxruntime 1.15.1
packaging 23.1
protobuf 4.23.4
sympy 1.12