compiling a wxwidgets project with cmake on Windows

Run into issues building the simple hello world example from wxwidgets using cmake on Windows. On Linux, the default github cmake action did not need much modification. 

CMakeLists.txt

Linux cmake build workflow

But for building on Windows, we needed to add some env variables in the workflow

env:

  # Customize the CMake build type here (Release, Debug, RelWithDebInfo, etc.)

  BUILD_TYPE: Release

  WXWIN: C:/wxWidgets-3.2.6

  wxWidgets_ROOT_DIR: C:/wxWidgets-3.2.6

  wxWidgets_LIBRARIES: C:/wxWidgets-3.2.6/include

  wxWidgets_INCLUDE_DIRS: C:/wxWidgets-3.2.6/lib/vc14x_x64_dll

  ARCH: x64

or else the find_package would complain about not finding wxWidgets_LIBRARIES and wxWidgets_INCLUDE_DIRS

Also, 

cmake -G"Visual Studio 17 2022" -B ${{github.workspace}}/build -DCMAKE_BUILD_TYPE=${{env.BUILD_TYPE}}

to specify which version of Visual Studio to use - and for this version, the default toolset is 14.3 which is the one used to build this set of wxwidgets binaries.
https://docs.wxwidgets.org/3.2.1/plat_msw_binaries.html

But we also had to add a dummy main() to get rid of a linker error, but that breaks the Linux build. 

/home/runner/work/wxOCVWarp/wxOCVWarp/hello.cpp:78:5: error: conflicting declaration of C function ‘int main()’

   78 | int main() { return 0;}

      |     ^~~~

In file included from /usr/include/wx-3.0/wx/wx.h:25,

                 from /home/runner/work/wxOCVWarp/wxOCVWarp/hello.cpp:3:

/home/runner/work/wxOCVWarp/wxOCVWarp/hello.cpp:11:1: note: previous declaration ‘int main(int, char**)’

   11 | wxIMPLEMENT_APP(MyApp);

      | ^~~~~~~~~~~~~~~

gmake[2]: *** [CMakeFiles/OCVWarp.dir/build.make:79: CMakeFiles/OCVWarp.dir/hello.cpp.o] Error 1

gmake[1]: *** [CMakeFiles/Makefile2:87: CMakeFiles/OCVWarp.dir/all] Error 2

gmake: *** [Makefile:91: all] Error 2

So, wrapped an ifdef around the dummy main(), and all is well.

#ifdef _WIN64

int main() { return 0;}

#endif