Make runtime_loader heap use reserve_address_range (easy)

[waddlesplash]

Right now it tries to use resize_area, but without having used reserve_address_range first. This works in most cases because due to ASLR there's not likely to be anything just after the heap area. But it won't work in the case where ASLR is disabled, among others. Instead it should use reserve_address_range like other heaps do.