Remove redundant 'virtual' keywords from overridden methods

'virtual' is redundant when 'override' is present, so keep only
'override'.

Add t/t_dist_cppstyle.pl to check for this.

src/V3InstrCount.cpp

@@ -75,7 +75,7 @@ public:
         , m_osp{osp} {
         if (nodep) iterate(nodep);
     }
-    virtual ~InstrCountVisitor() override = default;
+    ~InstrCountVisitor() override = default;
 
     // METHODS
     uint32_t instrCount() const { return m_instrCount; }
@@ -117,7 +117,7 @@ private:
     }
 
     // VISITORS
-    virtual void visit(AstNodeSel* nodep) override {
+    void visit(AstNodeSel* nodep) override {
         // This covers both AstArraySel and AstWordSel
         //
         // If some vector is a bazillion dwords long, and we're selecting 1
@@ -128,7 +128,7 @@ private:
         const VisitBase vb{this, nodep};
         iterateAndNextNull(nodep->bitp());
     }
-    virtual void visit(AstSel* nodep) override {
+    void visit(AstSel* nodep) override {
         // Similar to AstNodeSel above, a small select into a large vector
         // is not expensive. Count the cost of the AstSel itself (scales with
         // its width) and the cost of the lsbp() and widthp() nodes, but not
@@ -137,13 +137,13 @@ private:
         iterateAndNextNull(nodep->lsbp());
         iterateAndNextNull(nodep->widthp());
     }
-    virtual void visit(AstSliceSel* nodep) override {  // LCOV_EXCL_LINE
+    void visit(AstSliceSel* nodep) override {  // LCOV_EXCL_LINE
         nodep->v3fatalSrc("AstSliceSel unhandled");
     }
-    virtual void visit(AstMemberSel* nodep) override {  // LCOV_EXCL_LINE
+    void visit(AstMemberSel* nodep) override {  // LCOV_EXCL_LINE
         nodep->v3fatalSrc("AstMemberSel unhandled");
     }
-    virtual void visit(AstConcat* nodep) override {
+    void visit(AstConcat* nodep) override {
         // Nop.
         //
         // Ignore concat. The problem with counting concat is that when we
@@ -163,7 +163,7 @@ private:
         // the widths of the operands (ignored here).
         markCost(nodep);
     }
-    virtual void visit(AstNodeIf* nodep) override {
+    void visit(AstNodeIf* nodep) override {
         const VisitBase vb{this, nodep};
         iterateAndNextNull(nodep->condp());
         const uint32_t savedCount = m_instrCount;
@@ -188,7 +188,7 @@ private:
             if (nodep->ifsp()) nodep->ifsp()->user4(0);  // Don't dump it
         }
     }
-    virtual void visit(AstNodeCond* nodep) override {
+    void visit(AstNodeCond* nodep) override {
         // Just like if/else above, the ternary operator only evaluates
         // one of the two expressions, so only count the max.
         const VisitBase vb{this, nodep};
@@ -213,7 +213,7 @@ private:
             if (nodep->expr2p()) nodep->expr2p()->user4(0);  // Don't dump it
         }
     }
-    virtual void visit(AstActive* nodep) override {
+    void visit(AstActive* nodep) override {
         // You'd think that the OrderLogicVertex's would be disjoint trees
         // of stuff in the AST, but it isn't so: V3Order makes an
         // OrderLogicVertex for each ACTIVE, and then also makes an
@@ -229,14 +229,14 @@ private:
         markCost(nodep);
         UASSERT_OBJ(nodep == m_startNodep, nodep, "Multiple actives, or not start node");
     }
-    virtual void visit(AstNodeCCall* nodep) override {
+    void visit(AstNodeCCall* nodep) override {
         const VisitBase vb{this, nodep};
         iterateChildren(nodep);
         m_tracingCall = true;
         iterate(nodep->funcp());
         UASSERT_OBJ(!m_tracingCall, nodep, "visit(AstCFunc) should have cleared m_tracingCall.");
     }
-    virtual void visit(AstCFunc* nodep) override {
+    void visit(AstCFunc* nodep) override {
         // Don't count a CFunc other than by tracing a call or counting it
         // from the root
         UASSERT_OBJ(m_tracingCall || nodep == m_startNodep, nodep,
@@ -249,7 +249,7 @@ private:
             iterateChildren(nodep);
         }
     }
-    virtual void visit(AstNode* nodep) override {
+    void visit(AstNode* nodep) override {
         const VisitBase vb{this, nodep};
         iterateChildren(nodep);
     }
@@ -276,12 +276,12 @@ public:
         UASSERT_OBJ(osp, nodep, "Don't call if not dumping");
         if (nodep) iterate(nodep);
     }
-    virtual ~InstrCountDumpVisitor() override = default;
+    ~InstrCountDumpVisitor() override = default;
 
 private:
     // METHODS
     string indent() const { return string(m_depth, ':') + " "; }
-    virtual void visit(AstNode* nodep) override {
+    void visit(AstNode* nodep) override {
         ++m_depth;
         if (unsigned costPlus1 = nodep->user4()) {
             *m_osp << "  " << indent() << "cost " << std::setw(6) << std::left << (costPlus1 - 1)