pgsql: Fix pg_iswcased() for some libc case mappings.

Fix pg_iswcased() for some libc case mappings.

Some C libraries, such as macOS libc, case-map characters that they do
not classify as upper or lower. ILIKE index scans could then miss
rows, because those characters stayed in the fixed prefix.

Introduced in 630706ced0. 43a948b7b25 fixed similar issues, but missed
this one.

Author: shihao zhong <zhong950419(at)gmail(dot)com>
Reviewed-by: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Reviewed-by: Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAGRkXqS6pr-hG-g=K6RTdRw53SnMZWz3iXvh_wi8rqLSf972sA@mail.gmail.com
Backpatch-through: 19

Branch
------
REL_19_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/75a5fef57d09d75cc082fc6ffe817fc0772ef89a

Modified Files
--------------
src/backend/utils/adt/pg_locale_libc.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)