Shared toom evaluation functions

[Niels Möller]

nisse at lysator.liu.se (Niels Möller) writes:

> bodrato at mail.dm.unipi.it writes:
>
>> Niels should revive its toom_eval_pm2.c... and use the new functions.
>
> I'm attaching the function. Unfortunately, my toom53 and toom62 using
> it doesn't pass the testsuite at the moment, so it needs a little
> debugging before committing. I'll see when I can get to that.

I've checked in a working function now, tested on x86_32 and x86_64.

Getting that function to take advantage ov addlsh2_n requires a slight
reorganization, doing the additions as

  ((... + a4)*4 + a2)*4 + a0

rather than

  a0 + 4*a2 + 16*a4 + ...

I also added missing prototype and name-mangling for mpn_addlsh_n to
gmp-impl.h and asm-defs.m4.

/Niels