Compile unittests with onnx2c.

And and compiler and link in the generated unit test network
as a separate object.

This to better mimic how the user uses onnx2c.

src/graph.h

@@ -27,7 +27,7 @@ class Graph {
 	void print_tensor(const Tensor *, std::ostream &dst);
 	void print_functions(std::ostream &destination);
 	void print_includes(std::ostream &dst);
-	void print_interface_function(std::ostream &dst);
+	void print_interface_function(std::ostream &dst, bool print_definition=true);
 
 	/* Create the onnx2c graph elements from the ONNX graph */
 	void processGraph(

src/graph_print.cc

@@ -127,7 +127,7 @@ void Graph::print_includes(std::ostream &dst)
 	}
 }
 
-void Graph::print_interface_function(std::ostream &dst)
+void Graph::print_interface_function(std::ostream &dst, bool definition)
 {
 	bool isfirst = true;
 	// TODO: take the interface function name from the ONNX file name
@@ -162,7 +162,14 @@ void Graph::print_interface_function(std::ostream &dst)
 		}
 	}
 
-	dst << ") {" << std::endl;
+	dst << ")";
+	if( !definition ) { // not definition, i.e. decalaration
+		dst << ";" << std::endl;
+		return;
+	}
+
+	// else: definition - print the rest
+	dst << "{" << std::endl;
 
 	// since nodes were resolved from graph inputs in the order there were
 	// node inputs resolved, the nodes vector is now sorted in order so that