[9fans] avx2 encoding

[erik quanstrom]

at the risk of a second dumb question of the day, i'm looking at

        MOVQQU  -32(SI)(BX*1), X7

which generates the diagnostic

memmove4: doasm: notfound from=91 to=3b (220)   [aname 666]     -32(SI)(BX*1),X7

i tend to trust the compiler, but the verbage in the manual is a bit obtuse, and
i haven't yet gone through the vex/256 encoding in detail, but it looks like
the sib byte is still in there.  is this just an oversight?

- erik