G-1050 should not apply to check constraints.

Check constraints only accept literals, sql-functions (not PL/SQL) and references to columns in same row.
seesection "Restrictions on Check Constraints"

createtablet (    cchar(1) defaultonnull'Y'not null,constraint t_c_chkcheck (cin ('Y','N')));

results in

Warning (3,37): G-1050: Avoid using literals in your code