Better unused warning suppression.

The (k=k) can results in "multiple unsequenced modifications to 'kind'"
warning when this macro is expanded twice in the same expression.

Cython/Utility/ModuleSetupCode.c

@@ -157,8 +157,8 @@
   #define __Pyx_PyUnicode_READ_CHAR(u, i) ((Py_UCS4)(PyUnicode_AS_UNICODE(u)[i]))
   #define __Pyx_PyUnicode_KIND(u)         (sizeof(Py_UNICODE))
   #define __Pyx_PyUnicode_DATA(u)         ((void*)PyUnicode_AS_UNICODE(u))
-  /* (k=k) => avoid unused variable warning due to macro: */
-  #define __Pyx_PyUnicode_READ(k, d, i)   ((k=k), (Py_UCS4)(((Py_UNICODE*)d)[i]))
+  /* (void)(k) => avoid unused variable warning due to macro: */
+  #define __Pyx_PyUnicode_READ(k, d, i)   ((void)(k), (Py_UCS4)(((Py_UNICODE*)d)[i]))
 #endif
 
 #define __Pyx_PyString_FormatSafe(a, b)  ((unlikely((a) == Py_None)) ? PyNumber_Remainder(a, b) : __Pyx_PyString_Format(a, b))