Basically just copied all the amd64 files, removed all the *Q ops,
and rebuilt.

Compiles fib successfully.

Still need to do:
 - all the 64->32 bit op translations.
 - audit for instructions that aren't available on 386.
 - GO386=387?

Update #16358

Change-Id: Ib8c684586416a554a527a5eefa0cff71424e36f5
Reviewed-on: https://go-review.googlesource.com/24912
Reviewed-by: Cherry Zhang <cherryyz@google.com>

Last part of the 386 SSA port.

Modify the x86 backend to simulate SSE registers and
instructions with 387 registers and instructions.
The simulation isn't terribly performant, but it works,
and the old implementation wasn't very performant either.
Leaving to people who care about 387 to optimize if they want.

Turn on SSA backend for 386 by default.

Fixes #16358

Change-Id: I678fb59132620b2c47e993c1c10c4c21135f70c0
Reviewed-on: https://go-review.googlesource.com/25271
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>