[Reassociate] Canonicalize operands of vector binary operators.

Prior to this commit fmul and fadd binary operators were being canonicalized for
both scalar and vector versions.  We now canonicalize add, mul, and, or, and xor
vector instructions.
Tentatively appease the bots.

If this workaround gets the bots green, then we have to find out
why the -dwarf-accel-tables=Enable option doesn't work as
expected on non-darwin platforms.