AppVeyor tests for mingw32, mingw64, clang
AppVeyor tests for mingw32, mingw64, clang

ds77/zstd,inikep/zstd,Cyan4973/zstd,inikep/zstd,Majlen/zstd,inikep/zstd,Majlen/zstd,Majlen/zstd,Cyan4973/zstd,ds77/zstd,ds77/zstd,Cyan4973/zstd,Cyan4973/zstd,Majlen/zstd,ds77/zstd,Cyan4973/zstd,inikep/zstd