Avoid function call overhead of pg_popcount() in syslogger.c.

Instead of calling the pg_popcount() function for a single byte, we
can look up the value in the pg_number_of_ones array.

Discussion: https://postgr.es/m/20240401221117.GB2362108%40nathanxps13

src/backend/postmaster/syslogger.c

@@ -898,7 +898,7 @@ process_pipe_input(char *logbuffer, int *bytes_in_logbuffer)
 		if (p.nuls[0] == '\0' && p.nuls[1] == '\0' &&
 			p.len > 0 && p.len <= PIPE_MAX_PAYLOAD &&
 			p.pid != 0 &&
-			pg_popcount((char *) &dest_flags, 1) == 1)
+			pg_number_of_ones[dest_flags] == 1)
 		{
 			List	   *buffer_list;
 			ListCell   *cell;