lib:ldb: Use ldb_ascii_toupper() for case folding

lib:ldb: Use ldb_ascii_toupper() for case folding

For example there are at least two locales (tr_TR and az_AZ) in glibc
having dotless i transformation different from Latin scripts and GUID
versus Guid comparison would be different there (attribute name would
not match in the test).

See also
https://en.wikipedia.org/wiki/Dotted_and_dotless_I
https://lists.samba.org/archive/samba-technical/2019-December/134659.html

This fixes: LC_ALL=tr_TR.UTF-8 make test

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15248

Signed-off-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>