appveyor: disable zlib-ng build
appveyor: disable zlib-ng build

MSVC seems to have trouble with the ZEXTERN definition.

quixdb/squash,Cloudef/squash,jibsen/squash,Cloudef/squash,quixdb/squash,jibsen/squash,jibsen/squash,quixdb/squash,Cloudef/squash