neon/cgt: change all_set variables to sign_bit
neon/cgt: change all_set variables to sign_bit

I screwed this up during the merge; the original patch used sign_bits,
but I had a brain fart and was thinking INT*_MIN == ~0 so I changed
them to use ~0 (which I think is much more readable).  I realized my
mistake pretty quickly and changed the values back, but it seems I
forgot to change the variables back too :(

nemequ/simde,nemequ/simde,nemequ/simde