Add type confusion protection to the default memory provider.

src/mem/largealloc.h

@@ -405,5 +405,8 @@ namespace snmalloc
    * The memory provider that will be used if no other provider is explicitly
    * passed as an argument.
    */
-  inline GlobalVirtual default_memory_provider;
+  inline GlobalVirtual& default_memory_provider()
+  {
+    return TypedSingleton<GlobalVirtual>::global;
+  }
 } // namespace snmalloc