Avoid creating unused "__defaults__" getter functions for fused dispatch function. (GH-3491)

Closes GH-3481.

Cython/Compiler/ExprNodes.py

@@ -9279,7 +9279,8 @@ class PyCFunctionNode(ExprNode, ModuleNameMixin):
                             value=arg.default)
                         for arg in default_kwargs])
                     self.defaults_kwdict = defaults_kwdict.analyse_types(env)
-            else:
+            elif not self.specialized_cpdefs:
+                # Fused dispatch functions do not support (dynamic) default arguments, only the specialisations do.
                 if default_args:
                     defaults_tuple = DefaultsTupleNode(
                         self.pos, default_args, self.defaults_struct)
@@ -9440,8 +9441,7 @@ class PyCFunctionNode(ExprNode, ModuleNameMixin):
         if self.defaults_kwdict:
             code.putln('__Pyx_CyFunction_SetDefaultsKwDict(%s, %s);' % (
                 self.result(), self.defaults_kwdict.py_result()))
-        if def_node.defaults_getter and not self.specialized_cpdefs:
-            # Fused functions do not support dynamic defaults, only their specialisations can have them for now.
+        if def_node.defaults_getter:
             code.putln('__Pyx_CyFunction_SetDefaultsGetter(%s, %s);' % (
                 self.result(), def_node.defaults_getter.entry.pyfunc_cname))
         if self.annotations_dict:

Cython/Compiler/FusedNode.py

@@ -640,7 +640,7 @@ class FusedCFuncDefNode(StatListNode):
 
         pyx_code.put_chunk(
             u"""
-                def __pyx_fused_cpdef(signatures, args, kwargs, defaults, *, _fused_sigindex={}):
+                def __pyx_fused_cpdef(signatures, args, kwargs, defaults, _fused_sigindex={}):
                     # FIXME: use a typed signature - currently fails badly because
                     #        default arguments inherit the types we specify here!