zig winmain error

winmain1.zig

// runs WinMain using this WinMainCRTStartup

const HANDLE = *c_void;
const LPCTSTR = [*c]const u8;
const UINT = c_uint;
const HINSTANCE = ?*@OpaqueType();
const HMODULE = ?*@OpaqueType();
const PWSTR = [*c]u16;
const INT = c_int;

extern "kernel32" stdcallcc fn GetModuleHandleA(lpModuleName: ?[*]const u8) HINSTANCE;

extern "user32" stdcallcc fn MessageBoxA(hWnd: ?HANDLE, lpText: ?LPCTSTR, lpCaption: ?LPCTSTR, uType: UINT) c_int;
pub extern "kernel32" stdcallcc fn ExitProcess(exit_code: UINT) noreturn;

export stdcallcc fn WinMain(hInstance: HINSTANCE, hPrevInstance: HINSTANCE, lpCmdLine: PWSTR, nCmdShow: INT) UINT {
    _ = MessageBoxA(null, c"hello", c"title", 0);
    return 0;
}

export fn WinMainCRTStartup() noreturn {
    @setAlignStack(16);
    const result = WinMain(GetModuleHandleA(null), null, null, 0);
    ExitProcess(result);
}

winmain2.zig

// error: exported symbol collision: 'WinMainCRTStartup'
// error: root source file has no member called 'main'

const HANDLE = *c_void;
const LPCTSTR = [*c]const u8;
const UINT = c_uint;
const HINSTANCE = ?*@OpaqueType();
const HMODULE = ?*@OpaqueType();
const PWSTR = [*c]u16;
const INT = c_int;

extern "kernel32" stdcallcc fn GetModuleHandleA(lpModuleName: ?[*]const u8) HINSTANCE;

extern "user32" stdcallcc fn MessageBoxA(hWnd: ?HANDLE, lpText: ?LPCTSTR, lpCaption: ?LPCTSTR, uType: UINT) c_int;
pub extern "kernel32" stdcallcc fn ExitProcess(exit_code: UINT) noreturn;

export stdcallcc fn WinMain(hInstance: HINSTANCE, hPrevInstance: HINSTANCE, lpCmdLine: PWSTR, nCmdShow: INT) UINT {
    _ = MessageBoxA(null, c"hello", c"title", 0);
    return 0;
}

export stdcallcc fn WinMainCRTStartup() noreturn {
    @setAlignStack(16);
    const result = WinMain(GetModuleHandleA(null), null, null, 0);
    ExitProcess(result);
}

winmain3.zig

// runs WinMain using bootstrap.WinMainCRTStartup

const HANDLE = *c_void;
const LPCTSTR = [*]const u8;
const UINT = c_uint;
const HINSTANCE = *@OpaqueType();
const HMODULE = *@OpaqueType();
const PWSTR = [*]u16;
const INT = c_int;

extern "kernel32" stdcallcc fn GetModuleHandleA(lpModuleName: ?[*]const u8) HINSTANCE;
extern "user32" stdcallcc fn MessageBoxA(hWnd: ?HANDLE, lpText: ?LPCTSTR, lpCaption: ?LPCTSTR, uType: UINT) c_int;
extern "kernel32" stdcallcc fn ExitProcess(exit_code: UINT) noreturn;

export fn WinMain(hInstance: ?HINSTANCE, hPrevInstance: ?HINSTANCE, lpCmdLine: ?PWSTR, nCmdShow: INT) UINT {
    _ = MessageBoxA(null, c"hello", c"title", 0);
    return 0;
}

export fn WinMainCRTStartup() noreturn {
    @setAlignStack(16);
    const result = WinMain(GetModuleHandleA(null), null, null, 0);
    ExitProcess(result);
}

winmain4.zig

// runs WinMain using bootstrap.WinMainCRTStartup

const HANDLE = *c_void;
const LPCTSTR = [*]const u8;
const UINT = c_uint;
const HINSTANCE = *@OpaqueType();
const HMODULE = *@OpaqueType();
const PWSTR = [*]u16;
const INT = c_int;

extern "kernel32" stdcallcc fn GetModuleHandleA(lpModuleName: ?[*]const u8) HINSTANCE;
extern "user32" stdcallcc fn MessageBoxA(hWnd: ?HANDLE, lpText: ?LPCTSTR, lpCaption: ?LPCTSTR, uType: UINT) c_int;
extern "kernel32" stdcallcc fn ExitProcess(exit_code: UINT) noreturn;

export fn WinMain(hInstance: ?HINSTANCE, hPrevInstance: ?HINSTANCE, lpCmdLine: ?PWSTR, nCmdShow: INT) UINT {
    _ = MessageBoxA(null, c"hello", c"title", 0);
    return 0;
}

export stdcallcc fn WinMainCRTStartup() noreturn {
    @setAlignStack(16);
    const result = WinMain(GetModuleHandleA(null), null, null, 0);
    ExitProcess(result);
}