C++: Silence some more bogus consistency errors in syntax zoo

These were due to several functions occurring that would have the same TRAP key.
By making the functions static or wrapping the defining class in an anonymous
namespace the TRAP keys will differ from each other.

cpp/ql/test/library-tests/syntax-zoo/cpp11.cpp

@@ -138,7 +138,7 @@ namespace synthetic_dtor_calls {
   // This function is interesting because its extractor CFG has unreachable
   // calls to `c2.~C()` and `c3.~C()`. It's the calls that would have come from
   // leaving the block of `c2` by falling off the end, but no path does that.
-  int g(int x) {
+  static int g(int x) {
     do {
       C c1;
       if (x > 0) {