Fix sigset_t not found in liburing.h

Signed-off-by: Jiahao XU <Jiahao_XU@outlook.com>
diff --git a/src/include/liburing.h b/src/include/liburing.h
index 90403bc..a63c22b 100644
--- a/src/include/liburing.h
+++ b/src/include/liburing.h
@@ -2,6 +2,10 @@
 #ifndef LIB_URING_H
 #define LIB_URING_H
 
+#ifndef _XOPEN_SOURCE
+#define _XOPEN_SOURCE 500 /* Required for glibc to expose sigset_t */
+#endif
+
 #include <sys/socket.h>
 #include <sys/uio.h>
 #include <sys/stat.h>