Undefined reference `WinMain@16' c++

Hi, the command is as follows:

gcc -o main.dll dllmain.o -L/c/Users/Androide/Desktop/colo/pupa/dllmain/ -lSDL -lSDLmain -lmingw32

I get the error when compiling my project, the error is as follows:

> $ gcc -o main.dll dllmain.o
> -L/c/Users/Androide/Desktop/colo/pupa/dllmain/ -lSDL -lSDLmain -lmingw32 C:/msys32/mingw32/bin/../lib/gcc/i686-w64-mingw32/6.3.0/../../../../i686-w64-mingw32/lib/../lib/libmingw32.a(lib32_libmingw32_a-crt0_c.o):
> In function `main':
> C:/repo/mingw-w64-crt-git/src/mingw-w64/mingw-w64-crt/crt/crt0_c.c:18:
> undefined reference to `WinMain@16' collect2.exe: error: ld returned 1
> exit status

A screenshot of how I did it:

And the code of my dll that I am compiling:

#include "stdafx.h"
#include <SDL/SDL.h>
#include <windows.h>

extern "C" __declspec (dllexport) void __cdecl HelloWorld()
{
    //Show a message box with the text "Hello World"
    MessageBox(NULL, TEXT("Hello World"), TEXT("In a DLL"), MB_OK);
}


BOOL APIENTRY DllMain( HMODULE hModule,
                       DWORD  ul_reason_for_call,
                       LPVOID lpReserved
                     )
{
    //Different behaviors depending on the reason why DllMain is called
    switch (ul_reason_for_call) {
        case DLL_PROCESS_ATTACH:
            HelloWorld();
            break;
        case DLL_PROCESS_DETACH:
            HelloWorld();
            break;
        case DLL_THREAD_ATTACH:
            break;
        case DLL_THREAD_DETACH:
            break;
    }

    return TRUE;
}

It seems that linking to -LSDL could solve it but it didn't work for me.