Add pg_attribute_noreturn() to all the main routines of bgworkers

Those routines should never return and exit properly, so mark them
as such as a saity measure.

count_relations/count_relations.c

@@ -34,7 +34,7 @@
 PG_MODULE_MAGIC;
 void _PG_init(void);
-void count_relations_main(Datum main_arg);
+void count_relations_main(Datum main_arg) pg_attribute_noreturn();
 static volatile sig_atomic_t got_sigterm = false;

hello_notify/hello_notify.c

@@ -32,7 +32,7 @@
 PG_MODULE_MAGIC;
 void _PG_init(void);
-void hello_notify_main(Datum main_arg);
+void hello_notify_main(Datum main_arg) pg_attribute_noreturn();
 /* Worker name */
 static const char *hello_notify_name = "hello_notify";

hello_signal/hello_signal.c

@@ -25,7 +25,7 @@ PG_MODULE_MAGIC;
 /* Entry point of library loading */
 void _PG_init(void);
-void hello_main(Datum main_arg);
+void hello_main(Datum main_arg) pg_attribute_noreturn();
 /* SIGTERM handling */
 static volatile sig_atomic_t got_sigterm = false;

hello_world/hello_world.c

@@ -26,7 +26,7 @@ PG_MODULE_MAGIC;
 /* Entry point of library loading */
 void _PG_init(void);
 /* Main loop of process */
-void hello_main(Datum main_arg)
+void hello_main(Datum main_arg) pg_attribute_noreturn();
 /* Signal handling */
 static volatile sig_atomic_t got_sigterm = false;

kill_idle/kill_idle.c

@@ -31,7 +31,7 @@ PG_MODULE_MAGIC;
 /* Entry point of library loading */
 void _PG_init(void);
-void kill_idle_main(Datum main_arg);
+void kill_idle_main(Datum main_arg) pg_attribute_noreturn();
 /* Signal handling */
 static volatile sig_atomic_t got_sigterm = false;