numcmp: jit more work on cmp, still broken

wip: the DBL check is wrong.

fix access to the double value, offset 8
fix several opcodes: cvtsi2sd %rdx, %xmm0. movsd-0x8(%rbp), %xmm0
fix wrong description of ucomisd %xmm1, %xmm0.
forgot to shift %rax for the int case.

debug: disable decl. for yet unused variables.
potion_num_cmp: optimize, do not check dbl twice.