feat: add support for return statements in asmGenerator

src/main/wacc/backend/asmGenerator.scala

@@ -117,6 +117,8 @@ object asmGenerator {
           body.flatMap(generateStmt) ++
           List(Jump(LabelArg(startLabel)), LabelDef(endLabel))
       }
+      case microWacc.Return(expr) =>
+        evalExprIntoReg(expr, Register(RegSize.R64, RegName.AX))
       case _ => List()
     }