For x86 builds, try to detect SSE2 availability early and bail out

...instead of potentially just crashing. This is for the rare case
of somebody trying to run a QML2 based application on a Pentium 3
from before 2001 or older.

Change-Id: Ia5606fe28ef5579654ec939c86830af70dbb84d7
Reviewed-by: Kai Koehne <kai.koehne@digia.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>