Restored EndGameMenu as a pseudo-class

Fixes the following error: Attempting to open menu of unknown type 'EndGameMenu'
At least Adventures of Square is using this class in main menu

src/menu/menu.cpp

@@ -411,6 +411,11 @@ void M_SetMenu(FName menu, int param)
 		C_DoCommand("menu_quit");
 		return;
 
+	case NAME_EndGameMenu:
+		// The separate menu class no longer exists but the name still needs support for existing mods.
+		void ActivateEndGameMenu();
+		ActivateEndGameMenu();
+		return;
 	}
 
 	// End of special checks

src/menu/messagebox.cpp

@@ -125,17 +125,8 @@ CCMD (menu_quit)
 //
 //=============================================================================
 
-CCMD (menu_endgame)
+void ActivateEndGameMenu()
-{	// F7
+{
-	if (!usergame)
-	{
-		S_Sound (CHAN_VOICE | CHAN_UI, "menu/invalid", snd_menuvolume, ATTN_NONE);
-		return;
-	}
-		
-	//M_StartControlPanel (true);
-	S_Sound (CHAN_VOICE | CHAN_UI, "menu/activate", snd_menuvolume, ATTN_NONE);
-
 	FString tempstring = GStrings(netgame ? "NETEND" : "ENDGAME");
 	DMenu *newmenu = CreateMessageBoxMenu(CurrentMenu, tempstring, 0, false, NAME_None, []()
 	{
@@ -149,6 +140,20 @@ CCMD (menu_endgame)
 	M_ActivateMenu(newmenu);
 }
 
+CCMD (menu_endgame)
+{	// F7
+	if (!usergame)
+	{
+		S_Sound (CHAN_VOICE | CHAN_UI, "menu/invalid", snd_menuvolume, ATTN_NONE);
+		return;
+	}
+		
+	//M_StartControlPanel (true);
+	S_Sound (CHAN_VOICE | CHAN_UI, "menu/activate", snd_menuvolume, ATTN_NONE);
+
+	ActivateEndGameMenu();
+}
+
 //=============================================================================
 //
 //

src/namedef.h

@@ -671,6 +671,7 @@ xx(Optionsmenu)
 xx(Quitmenu)
 xx(Savemenu)
 xx(Playermenu)
+xx(EndGameMenu)
 
 xx(Playerbox)
 xx(Team)