Compiling C++ GUI for Windows (on macOS)

I'm using macOS Catalina (v10.15.7) to compile the following example code from gtkmm's online book:

#include <gtkmm.h>

int main(int argc, char *argv[])
{
    auto app = Gtk::Application::create(argc, argv, "org.gtkmm.examples.base");
    Gtk::Window window;
    window.set_default_size(200, 200);
    return app->run(window);
}

It compiles fine for macOS, but if I try to compile it for Windows using:

x86_64-w64-mingw32-g++ -o app.exe main.cpp -std=c++11 `pkg-config gtkmm-3.0 --cflags --libs`

Besides various warnings, I get the following errors for which I couldn't find almost any solutions on Google and Stack Overflow:

/usr/local/Cellar/glib/2.66.2_1/include/glib-2.0/gio/gcredentials.h:75:1: error: 'uid_t' does not name a type; did you mean 'pid_t'?
   75 | uid_t            g_credentials_get_unix_user      (GCredentials    *credentials,
      | ^~~~~
      | pid_t
/usr/local/Cellar/glib/2.66.2_1/include/glib-2.0/gio/gcredentials.h:79:52: error: 'uid_t' has not been declared
   79 |                                                    uid_t           uid,
      |                                                    ^~~~~
/usr/local/Cellar/glibmm/2.64.5/include/giomm-2.4/giomm/credentials.h:243:3: error: 'uid_t' does not name a type; did you mean 'pid_t'?
  243 |   uid_t get_unix_user();
      |   ^~~~~
      |   pid_t
/usr/local/Cellar/glibmm/2.64.5/include/giomm-2.4/giomm/credentials.h:264:22: error: 'uid_t' has not been declared
  264 |   bool set_unix_user(uid_t uid);
      |                      ^~~~~

Any help is much appretiated.

Solution

From an element chat room, I was told that the pkg-config on macOS seems to be using the macOS version of its libraries for compiling. Even if compile-time errors like uid_t are resolved, the libraries wouldn't be able to link properly.

In the end, it was much easier to compile the executable directly on a Windows machine.

Download & install MSYS2.
After installation, update MSYS2:
pacman -Syu
Install gcc & mingw packages:
- For i686 machines:
  pacman -S mingw-w64-i686-gcc
- For x86_64 machine:
  pacman -S mingw-w64-x86_64-gcc
Install gtkmm libraries:
- For i686 machines:
  pacman -S mingw-w64-i686-gtkmm3
- For x86_64 machines:
  pacman -S mingw-w64-x86_64-gtkmm3
Install pkg-config:
pacman -S pkg-config
Now open mingw64.exe in C:/msys64 and navigate to the directory where the source code exists.

The final cavier, compile your source code using:

g++ -std=c++11 hello.cpp -o myApp $(pkg-config gtkmm-3.0 --cflags --libs | sed 's/ -I/ -isystem /g')