Sometimes pointers are casted to ULONG just to get an ID or tag - this
is fine for 32bit pointers, but 64bit pointers will truncate which might
result in not being so unique after all.
CRC-ing the pointer should yield a more likely to be unique 32bit value.
NULL is a special case that yields 0 instead of the CRC, so code that
handles IDs/Tags with value 0 differently will continue to work.
For 32bit builds, it just returns the pointer as ULONG.
23b6374e9a