Use the proper comparator in gbt_bit_ssup_cmp.

Use the proper comparator in gbt_bit_ssup_cmp.

If we're dealing with leaf entries, the function to call is bitcmp
not byteacmp.  Using byteacmp didn't lead to any obvious failure,
but it did result in sorting the entries in a way not matching the
datatype's actual sort order.  Hence the constructed index would be
less efficient than one would expect, and in particular worse than
what you got before this code was added in v18 (by commit e4309f73f).

We might want to recommend that users reindex btree_gist indexes
on bit/varbit columns.

Author: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Ayush Tiwari <ayushtiwari.slg01@gmail.com>
Discussion: https://postgr.es/m/AH*AvQCYKhQGVvPWi1GiU4oY.8.1781609375063.Hmail.3020001251@tju.edu.cn
Backpatch-through: 18