CAUSES INDEX CORRUPTION

Description: MYISAM index corruption occurs for bulk insert
and repair table which involves "repair by sorting"
algorithm.

Analysis: The index corruption happens because of the
incorrect sorting done by "my_qsort2()" in 5.7. This happens
for a bulk insert with more than 450001959 rows or repair
table with more than 450001959 rows. In 8.0, "my_qsort2()"
is replaced by std::sort() as part of Bug#25965593.

Fix:- Backported Bug#25965593 fix partially to ensure
MyISAM repair by sorting algorithm uses std::sort().