add useless type fd_mask. it's in the reserved namespace.

include/sys/select.h

@@ -15,6 +15,8 @@ extern "C" {
 
 #define FD_SETSIZE 1024
 
+typedef unsigned long fd_mask;
+
 typedef struct
 {
 	unsigned long fds_bits[FD_SETSIZE / 8 / sizeof(long)];