iscc: fix computation of (negative) fixed powers of a binary relation
Commit
barvinok-0.41.6-36-g028122eed (update isl for support
for recent versions of clang, Sat Mar 4 10:42:47 2023 +0100)
brought in isl commit
isl-0.25-105-g7aed8cab9 (no longer treat minus sign
as part of token value, Tue Aug 2 13:52:13 2022 +0200),
which affects the parsing of negative powers.
Take into account the separate sign.
Reported-by: Evghenii <eg0x52@gmail.com>
Signed-off-by: Sven Verdoolaege <sven.verdoolaege@gmail.com>