cmake DZ_HAVE_UNISTD_H examples

SsageParuders/Android_Native_Surface my_android_opencv/3rdparty/zlib/CMakeLists.txt :27 

add_definitions(-DZ_HAVE_UNISTD_H)

joachimBurket/esp32-opencv 3rdparty/zlib/CMakeLists.txt :27 

add_definitions(-DZ_HAVE_UNISTD_H)