Add MinGW-builds gcc 4.8.2 as Tier 2 platform

Since we now ship an installer with it it certainly qualifies
as Tier 2 (if not even Tier 1...)

This change does not apply to Qt 5.

Change-Id: I2cb5068867e46a42fb52c7cfdb365aa99937bb04
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>