- Added virtmemLock/Unlock, needed for atomic find-and-map operations
- Added virtmemFindAslr, which looks for a random free area in AslrRegion
- virtmemReserve still exists for legacy callers who rely on sequential
allocation in order to avoid race conditions from concurrent uses
- Added virtmemFindStack, which searches within StackRegion instead
- Removed virtmemReserveStack/FreeStack
- Changed shmem/thread/tmem/codememory-jit to use the new virtmem API
- Legacy jit still uses virtmemReserve