Well, clang is now failing on M1 Max. I guess we have to wait till the nice guys working in Epic Games fix all the issues, or get the code from a couple of days ago.
Thanks, anyway 
This is the issue, just in case someone cares about it:
node_attr_utils.cc.o
onnxruntime::fbs::utils::LoadAttributeOrtFormat(onnxruntime::fbs::Attribute const&, onnx::AttributeProto&, std::__1::unique_ptr<onnxruntime::Graph, std::__1::default_deleteonnxruntime::Graph >&, onnxruntime::Graph&, onnxruntime::Node&, onnxruntime::logging::Logger const&) in graph_flatbuffers_utils.cc.o
ld: symbol(s) not found for architecture arm64