include/poll.h: Remove un-named union from 'struct pollfd'. It is not required by OpenGroup.org and violates the NuttX C coding standard because it is not C89 compatible.

include/nuttx/compiler.h

@@ -269,6 +269,10 @@
 
 /* ISO C11 supports anonymous (unnamed) structures and unions, added in
  * GCC 4.6 (but might be suppressed with -std= option)
+ *
+ * CAREFUL: This can cause issues for shared data structures shared between
+ * C and C++ if the two versions do not support the same features.  Structures
+ * and unions can lose binary compatibility!
  */
 
 #  undef CONFIG_HAVE_ANONYMOUS_STRUCT

include/poll.h

@@ -114,24 +114,16 @@ typedef uint8_t pollevent_t;
 
 struct pollfd
 {
-  /* REVISIT:  Un-named unions are forbidden by the coding standard because
-   * they are not available in C89.
-   */
+  /* Standard field */
 
-#ifdef CONFIG_HAVE_ANONYMOUS_UNION
-  union
-  {
-    int        fd;      /* The descriptor being polled */
-    FAR void  *ptr;     /* The psock or file being polled */
-  };
-#else
   int          fd;      /* The descriptor being polled */
-  FAR void    *ptr;     /* The psock or file being polled */
-#endif
-
-  FAR sem_t   *sem;     /* Pointer to semaphore used to post output event */
   pollevent_t  events;  /* The input event flags */
   pollevent_t  revents; /* The output event flags */
+
+  /* Non-standard fields used internally by NuttX */
+
+  FAR void    *ptr;     /* The psock or file being polled */
+  FAR sem_t   *sem;     /* Pointer to semaphore used to post output event */
   FAR void    *priv;    /* For use by drivers */
 };