This should check if Qt provides zlib functions, and adds zlib dependency in case of zlibless Qt. Tested with Qt providing zlib functions only.
file(GLOB lua_src *.c *.h)
set(LIBRARY_OUTPUT_PATH ${EXECUTABLE_OUTPUT_PATH})
IF(APPLE)
set(build_type STATIC)
add_definitions(-DLUA_USE_LINUX)
add_library (lua ${build_type} ${lua_src})
ENDIF(APPLE)
IF(WIN32)
set(build_type SHARED)
add_definitions(-DLUA_BUILD_AS_DLL)
add_library (lua ${build_type} ${lua_src})
SET_TARGET_PROPERTIES(lua PROPERTIES PREFIX "")
install(TARGETS lua RUNTIME DESTINATION ${target_dir})
endif(WIN32)