Bug #30393: Test "group_by" fails with a difference in "row count"

and strategy (explain)
  
The fix for WL3527 adds tests that test if the index usage hints
combinations don't cause syntax errors.
The EXPLAIN for one of these tests can be affected by the size of the
rowid on the disk (affected by the presence of large file support). 
Fixed to avoid the platform dependent test result by removing the 
irrelevant columns from the EXPLAIN result.

mysql-test/r/group_by.result

@@ -1129,7 +1129,7 @@ ERROR 42000: You have an error in your SQL syntax; check the manual that corresp
 EXPLAIN SELECT a FROM t1 USE INDEX FOR JOIN (i2) 
 USE INDEX FOR GROUP BY (i2) GROUP BY a;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	index	NULL	i2	9	NULL	144	Using index
+1	SIMPLE	t1	#	NULL	i2	#	NULL	#	#
 EXPLAIN SELECT a FROM t1 FORCE INDEX FOR JOIN (i2) 
 FORCE INDEX FOR GROUP BY (i2) GROUP BY a;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra

mysql-test/t/group_by.test

@@ -828,6 +828,11 @@ EXPLAIN SELECT a FROM t1 USE INDEX (i2) USE INDEX ();
 EXPLAIN SELECT a FROM t1 FORCE INDEX ();
 --error ER_PARSE_ERROR
 EXPLAIN SELECT a FROM t1 IGNORE INDEX ();
+# disable the columns irrelevant to this test here. On some systems 
+# without support for large files the rowid is shorter and its size affects 
+# the cost calculations. This causes the optimizer to choose loose index
+# scan over normal index access.
+--replace_column 4 # 7 # 9 # 10 #
 EXPLAIN SELECT a FROM t1 USE INDEX FOR JOIN (i2) 
   USE INDEX FOR GROUP BY (i2) GROUP BY a;
 EXPLAIN SELECT a FROM t1 FORCE INDEX FOR JOIN (i2)