signal: Make struct sigevent compatible with glibc

This patch added compatible struct sigevent definition with glibc.

Signed-off-by: ouyangxiangzhen <[email protected]>

include/signal.h

@@ -337,19 +337,33 @@ union sigval
 
 typedef CODE void (*sigev_notify_function_t)(union sigval value);
 
-struct sigevent
+typedef struct sigevent
 {
   uint8_t      sigev_notify; /* Notification method: SIGEV_SIGNAL, SIGEV_NONE, or SIGEV_THREAD */
   uint8_t      sigev_signo;  /* Notification signal */
   union sigval sigev_value;  /* Data passed with notification */
 
+  union
+    {
 #ifdef CONFIG_SIG_EVTHREAD
-  sigev_notify_function_t sigev_notify_function;      /* Notification function */
-  FAR struct pthread_attr_s *sigev_notify_attributes; /* Notification attributes (not used) */
+      struct
+        {
+          /* Notification function */
+
+          sigev_notify_function_t _function;
+
+          /* Notification attributes (not used) */
+
+          FAR struct pthread_attr_s *_attribute;
+        } _sigev_thread;
 #endif
+      pid_t _tid; /* ID of thread to signal */
+    } _sigev_un;
+} sigevent_t;
 
-  pid_t        sigev_notify_thread_id; /* ID of thread to signal */
-};
+#define sigev_notify_function   _sigev_un._sigev_thread._function
+#define sigev_notify_attributes _sigev_un._sigev_thread._attribute
+#define sigev_notify_thread_id  _sigev_un._tid
 
 /* The following types is used to pass parameters to/from signal handlers */