Fix build after removal of an extra safe_string.h

Fix build after removal of an extra safe_string.h

Move of strcasecmp redefine to lib/util/safe_string.h in
https://gitlab.com/samba-team/samba/-/merge_requests/1507 broke build on
Fedora 33 with GCC 10.2.1 for those compilation units that use
ldb_att_cmp().

The reason for that is that ldb_attr_cmp() defined as

   #define ldb_attr_cmp(a, b) strcasecmp(a, b)

because attribute names restricted to be ASCII by RFC2251 (LDAPv3 spec).

A solution is to add

   #undef strcasecmp

to all source code files which use ldb_attr_cmp().

Signed-off-by: Alexander Bokovoy <ab@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Thu Oct  1 22:45:29 UTC 2020 on sn-devel-184