Avoid redefinition of _XOPEN_SOURCE

cwcwidth/wcwidth_compat.h

@@ -23,6 +23,12 @@
 #ifndef WCWIDTH_COMPAT_H
 #define WCWIDTH_COMPAT_H
 
+#include <pyconfig.h>
+
+#if !defined(_WIN32) && !defined(_XOPEN_SOURCE)
+#define _XOPEN_SOURCE
+#endif
+
 #include <wchar.h>
 
 #if defined(USE_MK_WCWIDTH)

setup.py

@@ -5,15 +5,12 @@ from setuptools import setup, Extension
 
 
 extension_sources = ["cwcwidth/_impl.pyx"]
+define_macros = []
 if platform.system() == "Windows":
     extension_sources.append("cwcwidth/wcwidth.c")
-    define_macros = [
+    define_macrosa.append(
         ("USE_MK_WCWIDTH", None),
-    ]
-else:
-    define_macros = [
-        ("_XOPEN_SOURCE", "600"),
-    ]
+    )
 
 ext_modules = [
     Extension(