The pageSize and pageMask are too short on WIN64
The pageSize and pageMask are too short on WIN64

Due to this, roundUpToPage is truncating addresses > 2^32
With MSVC, minAddress is > 2^32, and it then takes ages to generate a VirtualAlloc > minAddress (several minutes).

timfel/squeakvm,OpenSmalltalk/vm,timfel/squeakvm,timfel/squeakvm,OpenSmalltalk/vm,timfel/squeakvm,timfel/squeakvm,timfel/squeakvm,OpenSmalltalk/vm,OpenSmalltalk/vm,OpenSmalltalk/vm,OpenSmalltalk/vm,OpenSmalltalk/vm,timfel/squeakvm,timfel/squeakvm,OpenSmalltalk/vm