Commit 21d39168170c6833512c4a5f53985272741bd7e7 added the 64-bit
version, so qsizetype now works cross-platform. The casts were added to
make qtbase compile on commit df853fed66d891077ae2d04ecfa171d7e2cd5202.
Change-Id: I26b8286f61534f88b649fffd166c409c5c232230
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>