[cmake] Allow adding extra source files to the onnx lib (#1439)
[cmake] Allow adding extra source files to the onnx lib (#1439)

* [cmake] Allow adding extra source files to the onnx lib

By setting ONNX_SRCS before including onnx's cmake files

* fix

onnx/onnx,onnx/onnx,onnx/onnx,onnx/onnx