Misc internal coverage improvements.

src/V3Delayed.cpp

@@ -457,7 +457,7 @@ private:
         }
     }
 
-    virtual void visit(AstNodeFor* nodep) VL_OVERRIDE {
+    virtual void visit(AstNodeFor* nodep) VL_OVERRIDE {  // LCOV_EXCL_LINE
         nodep->v3fatalSrc(
             "For statements should have been converted to while statements in V3Begin");
     }