SSA CFG: add test for multi-return non-continuing function

Author: clonker

test/libyul/ssa/controlFlowGraph/multi_return_non_continuing_function.yul

@@ -0,0 +1,32 @@
+{
+    function reverter() -> a, b { revert(0, 0) }
+    // the cfg should reflect that reverter has two output variables although it cannot continue
+    let x, y := reverter()
+    sstore(x, y)
+}
+// ----
+// digraph SSACFG {
+// nodesep=0.7;
+// graph[fontname="DejaVu Sans"]
+// node[shape=box,fontname="DejaVu Sans"];
+//
+// Entry [label="Entry"];
+// Entry -> Block0_0;
+// Block0_0 [fillcolor="#FF746C", style=filled, label="\
+// Block 0; (0, max 0)\nLiveIn: \l\
+// LiveOut: \l\nUsed: \l\nv0 := reverter()\l\
+// v1 := v0.proj(0)\l\
+// v2 := v0.proj(1)\l\
+// "];
+// Block0_0Exit [label="Terminated"];
+// Block0_0 -> Block0_0Exit;
+// FunctionEntry_reverter_0 [label="function reverter:
+//  [2 returns] := reverter()"];
+// FunctionEntry_reverter_0 -> Block1_0;
+// Block1_0 [fillcolor="#FF746C", style=filled, label="\
+// Block 0; (0, max 0)\nLiveIn: \l\
+// LiveOut: \l\nUsed: \l\nrevert(0x00, 0x00)\l\
+// "];
+// Block1_0Exit [label="Terminated"];
+// Block1_0 -> Block1_0Exit;
+// }