Use the W version of the function were we can.

dlls/user/message.c

@@ -2281,7 +2281,7 @@ BOOL WINAPI PeekMessageW( MSG *msg_out, HWND hwnd, UINT first, UINT last, UINT f
     /* need to fill the window handle for WM_PAINT message */
     if (msg.message == WM_PAINT)
     {
-        if (IsIconic( msg.hwnd ) && GetClassLongA( msg.hwnd, GCL_HICON ))
+        if (IsIconic( msg.hwnd ) && GetClassLongW( msg.hwnd, GCL_HICON ))
         {
             msg.message = WM_PAINTICON;
             msg.wParam = 1;

windows/cursoricon.c

@@ -127,7 +127,7 @@ static void *map_fileW( LPCWSTR name )
                          OPEN_EXISTING, FILE_FLAG_RANDOM_ACCESS, 0 );
     if (hFile != INVALID_HANDLE_VALUE)
     {
-        hMapping = CreateFileMappingA( hFile, NULL, PAGE_READONLY, 0, 0, NULL );
+        hMapping = CreateFileMappingW( hFile, NULL, PAGE_READONLY, 0, 0, NULL );
         CloseHandle( hFile );
         if (hMapping)
         {

windows/winproc.c

@@ -777,7 +777,7 @@ INT WINPROC_MapMsg32ATo32W( HWND hwnd, UINT msg, WPARAM *pwparam, LPARAM *plpara
                 xs->lpszClass = xs->cs.lpszClass = usBuffer.Buffer;
             }
 
-            if (GetWindowLongA(hwnd, GWL_EXSTYLE) & WS_EX_MDICHILD)
+            if (GetWindowLongW(hwnd, GWL_EXSTYLE) & WS_EX_MDICHILD)
             {
                 MDICREATESTRUCTW *mdi_cs = (MDICREATESTRUCTW *)HeapAlloc(GetProcessHeap(), 0,
                                                                          sizeof(*mdi_cs));
@@ -962,7 +962,7 @@ LRESULT WINPROC_UnmapMsg32ATo32W( HWND hwnd, UINT msg, WPARAM wParam, LPARAM lPa
             if (xs->lpszName)  HeapFree( GetProcessHeap(), 0, xs->lpszName );
             if (xs->lpszClass) HeapFree( GetProcessHeap(), 0, xs->lpszClass );
 
-            if (GetWindowLongA(hwnd, GWL_EXSTYLE) & WS_EX_MDICHILD)
+            if (GetWindowLongW(hwnd, GWL_EXSTYLE) & WS_EX_MDICHILD)
             {
                 MDICREATESTRUCTW *mdi_cs = (MDICREATESTRUCTW *)xs->cs.lpCreateParams;
                 if (HIWORD(mdi_cs->szTitle))