timing_builder: fixes a tatum error with some symbiflow tests

Signed-off-by: Alessandro Comodi <[email protected]>

Author: acomodi

vpr/src/timing/timing_graph_builder.cpp

@@ -52,6 +52,7 @@ std::unique_ptr<TimingGraph> TimingGraphBuilder::timing_graph() {
 
 void TimingGraphBuilder::build() {
     tg_ = std::make_unique<tatum::TimingGraph>();
+    tg_->set_allow_dangling_combinational_nodes(true);
 
     for (AtomBlockId blk : netlist_.blocks()) {
         AtomBlockType blk_type = netlist_.block_type(blk);