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/Makefile.in

@@ -67,7 +67,6 @@ FAILING_CPP_TESTS := \
     cpp_basic \
     cpp_basic_class_var_pub_member_built_in \
     cpp_basic_global_var_built_in \
-    cpp_basic_global_var_class \
     cpp_basic_template_class \
     cpp_basic_template_function \
     cpp_namespace \

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;
 }