redeclared without dllimport attribute: previous dllimport ignored

[omarespanol]

Hello i'm trying to compile this project..

#include "C:\Users\Androide\Desktop\minhook\Dynamic\MinHook_133_src\include\MinHook.h"//MHook header
#include <iostream>
#include <windows.h>
#include <Commctrl.h>
#include <conio.h>//For getch
using namespace std;

typedef void (*SENDMESSAGEW)();//Typedef for the hooked function
static SENDMESSAGEW Basewritefoobar;//Backup of the originak fonction

LRESULT WINAPI SendMessageW(HWND hWnd, UINT Msg, WPARAM wParam, LPARAM lParam);

static const wchar_t *hiddenprocess=L"tusitio";

LRESULT WINAPI BSSSendMessageW(HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam)
{
    if ( msg == LVM_INSERTITEMW || msg == LVM_SETITEMW)//Intercepts LVM_INSERTITEM and LVM_SETITEM messages
    {
        if (!lstrcmpW(((LVITEMW*)lparam)->pszText, hiddenprocess))//The lparam is a LVITEM* struct.
        {
            return 0;//If the item name is the same as process we want to hide, we simply return 0 (and we do not call the real SendMessage function.
        }
        return 0;
    }
    return SendMessage(hwnd, msg, wparam, lparam);//Calls the real SendMessage function.
}

static bool Hook();

template <typename T>
inline MH_STATUS MH_CreateHookEx(void* target, void* const base, T** original)
{
    return MH_CreateHook(target, base, reinterpret_cast<void**>(original));
}

int main()
{
    if (!Hook())//Hook "Writefoobar"
    {
        cout << "Hook failed" << endl;
        return 1;
    }

    cout << "Press a key to exit" << endl;
    _getch();
    return 0;
}

bool Hook()
{
    if (MH_Initialize() != MH_OK)
    {
        return false;
    }

    if (MH_CreateHookEx((void*)&SendMessageW, (void*)&BSSSendMessageW, &Basewritefoobar) != MH_OK)
    {
        return FALSE;
    }
    return MH_EnableHook((void*)&SendMessageW) == MH_OK;
}

However show this error:

Dynamic.cpp:11:16: warning: 'LRESULT SendMessageW(HWND, UINT, WPARAM, LPARAM)' redeclared without dllimport attribute: previous dllimport ignored [-Wattributes]
LRESULT WINAPI SendMessageW(HWND hWnd, UINT Msg, WPARAM wParam, LPARAM lParam);
^~~~~~~~~~~~

Why happen this? What means redeclared without dllimport if i am not using dllimportant someone can explain me what is happening. And the second thing, i must to use dll import to solve this error or why happen?

[Thomas1965]

SendMessageW is declared in winuser.h already, so there is no need to declare it.