Fix format attribute for gp_fatal_log to avoid clang build warning (#1134)

Use pg_attribute_printf for gp_fatal_log format checking

Replace GNU printf attribute with pg_attribute_printf macro
for gp_fatal_log to improve code portability and consistency
with PostgreSQL coding conventions.

Author: yjhjstz

src/bin/pg_upgrade/util.c

@@ -273,7 +273,7 @@ check_ok(void)
  *  respected.
  */
 void
-gp_fatal_log(const char *fmt,...)  __attribute__ ((format (gnu_printf, 1, 2)));
+gp_fatal_log(const char *fmt,...)  pg_attribute_printf(1, 2);
 
 void
 gp_fatal_log(const char *fmt,...)