Merge pull request #14322 from ethereum/stackLayoutsForUnassignedReturnVariables

Account for unassigned return variables in stack layout generation.

test/libyul/evmCodeTransform/unassigned_return_variable.yul

@@ -0,0 +1,19 @@
+{
+  // This used to throw during stack layout generation.
+  function g(b,s) -> y {
+    y := g(b, g(y, s))
+  }
+}
+// ====
+// stackOptimization: true
+// ----
+//     /* "":0:111   */
+//   stop
+//     /* "":60:109   */
+// tag_1:
+//   pop
+//     /* "":99:100   */
+//   0x00
+//     /* "":97:104   */
+//   tag_1
+//   jump	// in