-mtune=generic for i386 backend

[Jan Hubicka]

> 
> 20k what? Bigger code size?  If yes measured how? Did you do any 

Yes, it is 20k bigger code.  It is measured by building SPECint
with -mtune=generic versus -mtune=i686/k8 (in 32bit/64bit mode).
This is somewhat unforutnate fact I want to play with a bit as followup,
but it naturaly comes with fact that our instruction choice is limited
to common ground of the two CPUs and K8 alignment+move based passing
conventions are themselves introducing pretty noticeable hit.

I didn't included relative growth, since I used statically linked
binaries (so I test proper fortran library as well).

Just for quick idea, 
from other runs I get the dynamic sizes of SPEC binaries 5MB (with
debugging), so it translates as sub 1% (modulo debugging).

> further measurements on how code size is impact from this?

Not yet, but I hope to get into it. 

Honza
> 
> Thanks,
> -Andi (looking forward to using this switch in the future)