CMake no longer defines WIN32 on Cygwin!

set(CMAKE_LEGACY_CYGWIN_WIN32 0) # Remove when CMake >= 2.8.4 is required
cmake_minimum_required(VERSION 3.1)

​​https://stackoverflow.com/questions/28683365/how-to-disable-warning-in-cmake-3-1-about-cygwin-win32-not-being-defined?rq=1​​

project(MyApplication)
set(CMAKE_LEGACY_CYGWIN_WIN32 0) # Remove when CMake >= 2.8.4 is required
cmake_minimum_required(VERSION 3.1)
set(CMAKE_CXX_STANDARD 11)

aux_source_directory(src SOURCE_FILES)
add_executable(hello src/hello.c)