It looks like my second commit, adding /warnaserror (the msbuild equivalent of -Werror), exposed a warning in the MSVC 2019 build. Will investigate ASAP.

The MSVC 2019 build warnings were introduced by #3449. The errors are all caused by memcpy operations from BYTE const * * to BYTE const * *. The compiler incorrectly believes the const qualifiers don't match.

This warning doesn't show up in the MSVC 2022 build, so I think it is a bug in MSVC 2019.

Example warning (which is an error now that we have /warnaserror): https://github.com/facebook/zstd/actions/runs/4147381724/jobs/7174208209#step:4:207

Fixed by adding void* casts to the destination of each offending memcpy.