[Lightning] prolog/leaf requires a prolog_{d, f}/leaf_{d, f} counterpart

[Paulo César Pereira de Andrade]

  Hi,

  My x86_64 patches to keep stack 16 bytes aligned, in
http://github.com/pcpa/lightning is not fully correct for jit functions, because
it only checks if the number of arguments is odd, before calculating the
stack offset of the first argument.
  This should most times be not an issue, but will be for example if receiving
an odd number of integer/float arguments, and an even number of the other
type, but running out of registers, and needing to put some arguments on
the stack.

  I will implement @subject, matching jit_prepare{,d,f} semantics, but maybe
I am missing something, so, commenting here :-)

  I am also still missing adding the logic and test cases for jit_allocai,
in both, the default/previous behavior of only receiving arguments on
registers, and now also for when receiving extra arguments on stack.

Thanks,
Paulo