The changes here are produced by modifying thirdparty/zstd/zstd_v.patch, and then running v thirdparty/zstd/update.vsh .

You can generate a new patch by: diff -u zstd-1.5.7/build/single_file_libs/zstd.c thirdparty/zstd/zstd.c > zstd_custom.patch

BTW, patch is between /* >> v_patch start */ and /* << v_patch end */ mostly.