Fix build warning for use of strdup in ultrajson (pandas-dev#48369)

Author: rgommers

pandas/_libs/src/headers/portable.h

@@ -1,8 +1,16 @@
 #ifndef _PANDAS_PORTABLE_H_
 #define _PANDAS_PORTABLE_H_
 
+// To get `strdup` from strings.h
+#ifndef _XOPEN_SOURCE
+#define _XOPEN_SOURCE 600
+#endif
+
+#include <string.h>
+
 #if defined(_MSC_VER)
 #define strcasecmp( s1, s2 ) _stricmp( s1, s2 )
+#define strdup _strdup
 #endif
 
 // GH-23516 - works around locale perf issues

pandas/_libs/src/ujson/lib/ultrajson.h

@@ -54,6 +54,7 @@ tree doesn't have cyclic references.
 
 #include <stdio.h>
 #include <wchar.h>
+#include "../../headers/portable.h"
 
 // Don't output any extra whitespaces when encoding
 #define JSON_NO_EXTRA_WHITESPACE