V4: temporarilly disable the optmizer/regalloc.

There are two bugs for which patches are pending. In order to unblock
qtquickcontrols, this code is disabled until those pending patches are
merged.

Change-Id: I2362bf3db0614ef8c6f45a1506838f227ea17b59
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>