Rule 2.4: Add a missing test case.

Author: lcartey

c/misra/test/rules/RULE-2-4/test.c

@@ -77,4 +77,8 @@ void testMacroNameNotUsed() {
   { int x; }
 
 struct s14 PARTIAL; // NON_COMPLIANT - affected by macro, but not fully
-                    // generated, so fair to report as unused
+                    // generated, so fair to report as unused
+
+typedef struct {
+  int x;
+} S15; // COMPLIANT - not a tag