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/conditional_destructors.cpp

@@ -26,7 +26,7 @@ class C2 {
     }
 };
 
-void f1(void) {
+static void f1(void) {
     if (C1(1) == C1(2)) {
         ;
     }
@@ -35,7 +35,7 @@ void f1(void) {
     }
 }
 
-void f2(void) {
+static void f2(void) {
     if (C2(1) == C2(2)) {
         ;
     }