torture:charset: use < and > assertions for strcasecmp_m

torture:charset: use < and > assertions for strcasecmp_m

strcasecmp_m is supposed to return a negative, zero, or positive
number, depending on whether the first argument is less than, equal to,
or greater than the second argument (respectively).

We have been asserting that it returns exactly the difference between
the codepoints in the first character that differs.

This fixes a knownfail on 32 bit.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15625

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>