OK - I guess that means your graphics chipset is not supported by the modesetting driver and it falls back to the vesa driver, which does not support rotation.
If you look in /var/log/Xorg.0.log, what do you see in this section: [ 8985.827] (==) Matched intel as autoconfigured driver 0
[ 8985.827] (==) Matched modesetting as autoconfigured driver 1
[ 8985.827] (==) Matched fbdev as autoconfigured driver 2
[ 8985.827] (==) Matched vesa as autoconfigured driver 3