Make sure strdup() is properly declared.

crypto/ui/ui_lib.c

@@ -56,6 +56,15 @@
  *
  */
 
+#include <openssl/e_os2.h>
+/* The following defines enable the declaration of strdup(), which is an
+   extended function according to X/Open. */
+#ifdef OPENSSL_SYS_VMS_DECC
+# define _XOPEN_SOURCE_EXTENDED
+#endif
+#ifdef OPENSSL_SYS_UNIX
+# define __USE_XOPEN_EXTENDED	/* For Linux and probably anything GNU */
+#endif
 #include <string.h>
 
 #include <openssl/ui.h>