Use _Noreturn (C11; GNU89) properly

A function that returns with no value is a different thing from a
function that doesn't return at all.  Those are two orthogonal
concepts, commonly confused.

pthread_create(3) expects a pointer to a start routine that has a
very precise prototype:

    void *(*start_routine)(void *);

However, other thread functions, such as kernel ones, expect:

    void (*start_routine)(void *);

Providing a different one is incorrect, and has only been working
because the ABIs happen to produce a compatible function.

We should use '_Noreturn void', since it's the natural type, and
then provide a '_Noreturn void *' wrapper for pthread functions.

For consistency, replace most cases of __NORETURN or
__attribute__((noreturn)) by _Noreturn.  _Noreturn is understood
by -std=gnu89, so it should be safe to use everywhere.

Ref: https://github.com/openzfs/zfs/pull/13110#discussion_r808450136
Ref: https://software.codidact.com/posts/285972
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Co-authored-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Signed-off-by: Alejandro Colomar <alx.manpages@gmail.com>
Closes #13120

module/zfs/dmu_send.c

@@ -1234,7 +1234,7 @@ redact_list_cb(redact_block_phys_t *rb, void *arg)
  * error code of the thread in case something goes wrong, and pushes the End of
  * Stream record when the traverse_dataset call has finished.
  */
-static void
+static _Noreturn void
 send_traverse_thread(void *arg)
 {
 	struct send_thread_arg *st_arg = arg;
@@ -1324,7 +1324,7 @@ get_next_range(bqueue_t *bq, struct send_range *prev)
 	return (next);
 }
 
-static void
+static _Noreturn void
 redact_list_thread(void *arg)
 {
 	struct redact_list_thread_arg *rlt_arg = arg;
@@ -1519,7 +1519,7 @@ find_next_range(struct send_range **ranges, bqueue_t **qs, uint64_t *out_mask)
  * data from the redact_list_thread and use that to determine which blocks
  * should be redacted.
  */
-static void
+static _Noreturn void
 send_merge_thread(void *arg)
 {
 	struct send_merge_thread_arg *smt_arg = arg;
@@ -1744,7 +1744,7 @@ enqueue_range(struct send_reader_thread_arg *srta, bqueue_t *q, dnode_t *dn,
  * some indirect blocks can be discarded because they're not holes. Second,
  * it issues prefetches for the data we need to send.
  */
-static void
+static _Noreturn void
 send_reader_thread(void *arg)
 {
 	struct send_reader_thread_arg *srta = arg;