Get rid of all warnings and errors on Windows.

This increases msvc compatibility.
The v0.8 support is a valid point, I'd forgotten about that.

AdjustAmountOfExternalAllocatedMemory() is a heuristic that (somewhat indirectly) tells the GC how often it should sweep. It's conceivable that you're doing large off-heap allocations and want those factored in.

Then again, that's probably not a very common use case.  When in doubt I usually take the reactionary approach: leave it as-is and don't do anything until the first bug report comes in.  I would suggest adding a comment that explains the rationale for using int.