Issue #4051: Prevent conflict of UNICODE macros in cPickle.

Misc/NEWS

@@ -286,6 +286,8 @@ C-API
 Extension Modules
 -----------------
 
+- Issue #4051: Prevent conflict of UNICODE macros in cPickle.
+
 - Issue #4228: Pack negative values the same way as 2.4 in struct's L format.
 
 - Issue #1040026: Fix os.times result on systems where HZ is incorrect.

Modules/cPickle.c

@@ -17,6 +17,14 @@ PyDoc_STRVAR(cPickle_module_documentation,
 /* Bump this when new opcodes are added to the pickle protocol. */
 #define HIGHEST_PROTOCOL 2
 
+/*
+ * Note: The UNICODE macro controls the TCHAR meaning of the win32 API. Since
+ * all headers have already been included here, we can safely redefine it.
+ */
+#ifdef UNICODE
+#  undef UNICODE
+#endif
+
 /*
  * Pickle opcodes.  These must be kept in synch with pickle.py.  Extensive
  * docs are in pickletools.py.