Account for extra uncommitted memory size also in ASSERTs.

The fix for the stack layout in applications that are loading .NET
libraries in addition did not update the assertions that make sure
that the actual end of the stack is where it should be.

Task-number: QTBUG-38067
Change-Id: Ib8be1228bc9f10baf8d3484bb280a3a5c8021ab8
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@digia.com>