wmain.c

#include <windows.h>

// https://docs.microsoft.com/en-us/cpp/build/reference/entry-entry-point-symbol
#pragma comment(linker, "/ENTRY:wWinMainCRTStartup")

extern int __cdecl main();

int wmain(int argc, wchar_t* argv[])
{
    char** args;
    int nbytes = sizeof(char*) * (argc + 1);
    HANDLE heap = GetProcessHeap();

    for (int i = 0; i < argc; ++i)
        nbytes += WideCharToMultiByte(CP_UTF8, 0, argv[i], -1, NULL, 0, NULL, NULL);

    args = HeapAlloc(heap, 0, nbytes);
    args[0] = (char*)(args + argc + 1);
    
    for (int i = 0; i < argc; ++i)
        args[i+1] = args[i] + WideCharToMultiByte(CP_UTF8, 0, argv[i], -1, args[i], nbytes, NULL, NULL);
    
    args[argc] = NULL;

    argc = main(argc, args);
    HeapFree(heap, 0, args);
    return argc;
}

int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPWSTR lpCmdLine, int nCmdShow)
{
    (void) hInstance;
    (void) hPrevInstance;
    (void) lpCmdLine;
    (void) nCmdShow;

    int argc;
    wchar_t** argv;
    argv = CommandLineToArgvW(GetCommandLineW(), &argc);
    argc = wmain(argc, argv);
    LocalFree(argv);
    return argc;
}