Foreign key definitions used in CREATE and ALTER TABLE statements
on InnoDB tables were ignored if these statements were wrapped in
conditional comments (like /*!50101 ... */ or /*! ... */).

The problem was caused by the fact that InnoDB did their own parsing
of foreign key definitions in order to validate them and store them
in its internal data-dictionary. And this parser didn't handle
conditional comments correctly.

Transition to new SQL-layer data-dictionary in 8.0 and removal of such
parsing by fix for bug#30287895 "REMOVE DICT_CREATE_FOREIGN_CONSTRAINTS()
AND FRIENDS" has solved this problem.

Test case only.

Reviewed-by: Gleb Shchepa <gleb.shchepa@oracle.com>