msvc 9 build tweak.

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@6626 d0543943-73ff-0310-b7d9-9358b9ac24b2

libs/apr/include/arch/win32/apr_arch_networkio.h

@@ -20,6 +20,9 @@
 #include "apr_network_io.h"
 #include "apr_general.h"
 #include "apr_poll.h"
+#ifdef _MSC_VER
+#undef MCAST_JOIN_SOURCE_GROUP
+#endif
 
 typedef struct sock_userdata_t sock_userdata_t;
 struct sock_userdata_t {