Fix large return blocks with --comp-limit-blocks (#4028).

src/V3DepthBlock.cpp

@@ -93,6 +93,7 @@ private:
         }
     }
     void visit(AstStmtExpr* nodep) override {}  // Stop recursion after introducing new function
+    void visit(AstJumpBlock*) override {}  // Stop recursion as can't break up across a jump
     void visit(AstNodeStmt* nodep) override {
         m_depth++;
         if (m_depth > v3Global.opt.compLimitBlocks()) {  // Already done