Use standard SIGTERM signal handler die() in test_shm_mq worker.

Previously test_shm_mq worker used the stripped-down version of die()
as the SIGTERM signal handler. This commit makes it use die(), instead,
to simplify the code.

In terms of the code, the difference between die() and the stripped-down
version previously used is whether the signal handler directly may call
ProcessInterrupts() or not. But this difference doesn't exist in
a background worker because, in bgworker, DoingCommandRead flag will
never be true and die() will never call ProcessInterrupts() directly.
Therefore test_shm_mq worker can safely use die(), like other bgworker
proceses (e.g., logical replication apply launcher or autoprewarm worker)
currently do.

Thanks to Craig Ringer for the report and investigation of the issue.

Author: Bharath Rupireddy
Reviewed-by: Fujii Masao
Discussion: https://postgr.es/m/CAGRY4nxsAe_1k_9g5b47orA0S011iBoHsXHFMH7cg7HV0O1bwQ@mail.gmail.com

src/test/modules/test_shm_mq/worker.c

@@ -24,10 +24,10 @@
 #include "storage/procarray.h"
 #include "storage/shm_mq.h"
 #include "storage/shm_toc.h"
+#include "tcop/tcopprot.h"
 
 #include "test_shm_mq.h"
 
-static void handle_sigterm(SIGNAL_ARGS);
 static void attach_to_queues(dsm_segment *seg, shm_toc *toc,
 							 int myworkernumber, shm_mq_handle **inqhp,
 							 shm_mq_handle **outqhp);
@@ -58,10 +58,9 @@ test_shm_mq_main(Datum main_arg)
 	 * Establish signal handlers.
 	 *
 	 * We want CHECK_FOR_INTERRUPTS() to kill off this worker process just as
-	 * it would a normal user backend.  To make that happen, we establish a
-	 * signal handler that is a stripped-down version of die().
+	 * it would a normal user backend.  To make that happen, we use die().
 	 */
-	pqsignal(SIGTERM, handle_sigterm);
+	pqsignal(SIGTERM, die);
 	BackgroundWorkerUnblockSignals();
 
 	/*
@@ -196,24 +195,3 @@ copy_messages(shm_mq_handle *inqh, shm_mq_handle *outqh)
 			break;
 	}
 }
-
-/*
- * When we receive a SIGTERM, we set InterruptPending and ProcDiePending just
- * like a normal backend.  The next CHECK_FOR_INTERRUPTS() will do the right
- * thing.
- */
-static void
-handle_sigterm(SIGNAL_ARGS)
-{
-	int			save_errno = errno;
-
-	SetLatch(MyLatch);
-
-	if (!proc_exit_inprogress)
-	{
-		InterruptPending = true;
-		ProcDiePending = true;
-	}
-
-	errno = save_errno;
-}