Make archiver's SIGQUIT handler exit via _exit().

Commit 8e19a826 changed the SIGQUIT handlers of almost all server
processes not to run atexit callbacks.  The archiver process was
skipped, perhaps because it's not connected to shared memory; but
it's just as true here that running atexit callbacks in a signal
handler is unsafe.  So let's make it work like the rest.

In HEAD and v13, we can use the common SignalHandlerForCrashExit
handler.  Before that, just tweak pgarch_exit to use _exit(2)
explicitly.

Like the previous commit, back-patch to all supported branches.

Kyotaro Horiguchi, back-patching by me

Discussion: https://postgr.es/m/1850884.1599601164@sss.pgh.pa.us

src/backend/postmaster/pgarch.c

@@ -96,7 +96,6 @@ static pid_t pgarch_forkexec(void);
 #endif
 
 NON_EXEC_STATIC void PgArchiverMain(int argc, char *argv[]) pg_attribute_noreturn();
-static void pgarch_exit(SIGNAL_ARGS);
 static void pgarch_waken(SIGNAL_ARGS);
 static void pgarch_waken_stop(SIGNAL_ARGS);
 static void pgarch_MainLoop(void);
@@ -229,7 +228,7 @@ PgArchiverMain(int argc, char *argv[])
 	pqsignal(SIGHUP, SignalHandlerForConfigReload);
 	pqsignal(SIGINT, SIG_IGN);
 	pqsignal(SIGTERM, SignalHandlerForShutdownRequest);
-	pqsignal(SIGQUIT, pgarch_exit);
+	pqsignal(SIGQUIT, SignalHandlerForCrashExit);
 	pqsignal(SIGALRM, SIG_IGN);
 	pqsignal(SIGPIPE, SIG_IGN);
 	pqsignal(SIGUSR1, pgarch_waken);
@@ -246,14 +245,6 @@ PgArchiverMain(int argc, char *argv[])
 	exit(0);
 }
 
-/* SIGQUIT signal handler for archiver process */
-static void
-pgarch_exit(SIGNAL_ARGS)
-{
-	/* SIGQUIT means curl up and die ... */
-	exit(1);
-}
-
 /* SIGUSR1 signal handler for archiver process */
 static void
 pgarch_waken(SIGNAL_ARGS)