py/objmodule: Workaround for MSVC with no module delegation.

When compiling mpy-cross, there is no `sys` module, and so there will
be no entries in the `mp_builtin_module_delegation_table`.

MSVC doesn't like this, so instead pretend as if the feature isn't
enabled at all.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

py/makemoduledefs.py

@@ -103,6 +103,9 @@ def generate_module_table_header(modules):
 
 
 def generate_module_delegations(delegations):
+    if not delegations:
+        return
+
     print("\n#define MICROPY_MODULE_DELEGATIONS \\")
     for obj_module, fun_name in delegations:
         print(