the amd64 compiler uses only SSE.

i thought about putting it in 8[acl] and might
have asked about that here, but i think i concluded
at the time that 64-bit would appear on all boards.
for 32-bit i wouldn't bother trying to mix the 387 and SSE,
so there would be two 386 environments, old and new,
which seemed a big nuisance.