flex_array: declare parts member to have incomplete type

The `parts' member of struct flex_array should evaluate to an incomplete
type so that sizeof() cannot be used and C99 does not require the
zero-length specification.

Signed-off-by: David Rientjes <rientjes@google.com>
Acked-by: Dave Hansen <dave@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/flex_array.h

@@ -21,7 +21,7 @@ struct flex_array {
 		struct {
 			int element_size;
 			int total_nr_elements;
-			struct flex_array_part *parts[0];
+			struct flex_array_part *parts[];
 		};
 		/*
 		 * This little trick makes sure that