[xmlrpc-c] Fix MacOS build

libs/xmlrpc-c/lib/abyss/src/server.c

@@ -1,6 +1,9 @@
 /* Copyright information is at end of file */
 
 #define _XOPEN_SOURCE 600  /* Make sure strdup() is in <string.h> */
+#ifdef __APPLE__
+#define _DARWIN_C_SOURCE
+#endif
 #define _BSD_SOURCE  /* Make sure setgroups()is in <grp.h> */
 #ifndef _DEFAULT_SOURCE
 #define _DEFAULT_SOURCE