Fix uninitialized-variable bug.

For some reason, neither of the compilers I usually use noticed the
uninitialized-variable problem I introduced in commit 7e2a18a916.
That's hardly a good enough excuse though.  Committing with brown paper bag
on head.

In addition to putting the operations in the right order, move the
declaration of "now" inside the loop; there's no need for it to be
outside, and that does wake up older gcc enough to notice any similar
future problem.

Back-patch to 9.4; earlier versions lack the time-to-SIGKILL stanza
so there's no bug.

src/backend/postmaster/postmaster.c

@@ -1601,8 +1601,7 @@ ServerLoop(void)
 {
 	fd_set		readmask;
 	int			nSockets;
-	time_t		now,
-				last_lockfile_recheck_time,
+	time_t		last_lockfile_recheck_time,
 				last_touch_time;
 
 	last_lockfile_recheck_time = last_touch_time = time(NULL);
@@ -1613,6 +1612,7 @@ ServerLoop(void)
 	{
 		fd_set		rmask;
 		int			selres;
+		time_t		now;
 
 		/*
 		 * Wait for a connection request to arrive.
@@ -1764,6 +1764,16 @@ ServerLoop(void)
 		Assert(pthread_is_threaded_np() == 0);
 #endif
 
+		/*
+		 * Lastly, check to see if it's time to do some things that we don't
+		 * want to do every single time through the loop, because they're a
+		 * bit expensive.  Note that there's up to a minute of slop in when
+		 * these tasks will be performed, since DetermineSleepTime() will let
+		 * us sleep at most that long; except for SIGKILL timeout which has
+		 * special-case logic there.
+		 */
+		now = time(NULL);
+
 		/*
 		 * If we already sent SIGQUIT to children and they are slow to shut
 		 * down, it's time to send them SIGKILL.  This doesn't happen
@@ -1782,15 +1792,6 @@ ServerLoop(void)
 			AbortStartTime = 0;
 		}
 
-		/*
-		 * Lastly, check to see if it's time to do some things that we don't
-		 * want to do every single time through the loop, because they're a
-		 * bit expensive.  Note that there's up to a minute of slop in when
-		 * these tasks will be performed, since DetermineSleepTime() will let
-		 * us sleep at most that long.
-		 */
-		now = time(NULL);
-
 		/*
 		 * Once a minute, verify that postmaster.pid hasn't been removed or
 		 * overwritten.  If it has, we force a shutdown.  This avoids having