fixed_typemap: implement need<> method

It may be used in constructors of other objects to assert a dependency.
It also helps to ensure reverse destruction order of that dependency.

rpcs3/Emu/VFS.cpp

@@ -29,11 +29,8 @@ struct vfs_manager
 
 bool vfs::mount(std::string_view vpath, std::string_view path)
 {
-	if (!g_fxo->get<vfs_manager>())
+	// Workaround
-	{
+	g_fxo->need<vfs_manager>();
-		// Init (TODO)
-		g_fxo->init<vfs_manager>();
-	}
 
 	const auto table = g_fxo->get<vfs_manager>();
 

rpcs3/util/fixed_typemap.hpp

@@ -148,6 +148,16 @@ namespace stx
 			}
 		}
 
+		// Check if object is not initialized but shall be initialized first (to use in initializing other objects)
+		template <typename T>
+		void need() noexcept
+		{
+			if (!get<T>())
+			{
+				init<T>();
+			}
+		}
+
 		// Explicitly (re)initialize object of type T possibly with dynamic type As and arguments
 		template <typename T, typename As = T, typename... Args>
 		As* init(Args&&... args) noexcept