* spot/misc/bitvect.cc, spot/misc/bitvect.hh, spot/misc/hash.hh,
spot/twa/acc.hh, spot/twaalgos/cobuchi.cc, spot/twaalgos/degen.cc,
spot/twaalgos/determinize.cc, spot/twaalgos/parity.cc,
spot/twaalgos/powerset.cc, spot/twaalgos/product.cc,
spot/twaalgos/stutter.cc, spot/twaalgos/totgba.cc,
spot/twaalgos/toweak.cc: Mark hash function as noexcept to please GCC
snapshot.