Fix isPure to be superset of isOutputter.

This may cause some additional SIDEEFFECT warnings that previously were not shown.

src/V3Ast.cpp

@@ -801,7 +801,6 @@ AstNode* AstNode::cloneTreeIter(bool needPure) {
                          << this->warnMore()
                          << "... Suggest use a temporary variable in place of this expression");
         // this->v3fatalSrc("cloneTreePure debug backtrace");  // Comment in to debug where caused
-        // it
     }
     AstNode* const newp = this->clone();
     if (this->m_op1p) newp->op1p(this->m_op1p->cloneTreeIterList(needPure));

src/V3AstNodeOther.h

@@ -2786,7 +2786,7 @@ public:
     bool isGateOptimizable() const override { return false; }
     bool isPredictOptimizable() const override { return false; }
     bool isOutputter() override { return true; }
-    // but isPure()  true
+    bool isPure() override { return false; }
     AstCoverDecl* declp() const { return m_declp; }  // Where defined
 };
 class AstCoverToggle final : public AstNodeStmt {
@@ -3379,7 +3379,7 @@ public:
     bool isGateOptimizable() const override { return false; }
     bool isPredictOptimizable() const override { return false; }
     bool isOutputter() override { return true; }
-    // but isPure()  true
+    bool isPure() override { return false; }
     AstTraceDecl* declp() const { return m_declp; }
     VTraceType traceType() const { return m_traceType; }
     uint32_t baseCode() const { return m_baseCode; }