Use wrapper functions for global variables of non-C types

Don't try to export the variables whose type can't be represented in C
directly, this can't work.

Instead, just let use the default implementation to generate wrapper functions
for them.

Update "cpp_basic_global_var_class" unit test accordingly and remove it from
the list of the failing tests.

Examples/test-suite/c/cpp_basic_global_var_class_runme.c

@@ -3,7 +3,7 @@
 
 int main(int argc, const char *argv[])
 {
-    assert(myGlobalClassInstance);
+    assert(myGlobalClassInstance_get());
 
     return 0;
 }