Add type confusion protection to the default memory provider.

src/mem/alloc.h

@@ -60,7 +60,7 @@ namespace snmalloc
    * variable.  This should be used from within the library or program that
    * owns the pagemap.
    *
-   * This class makes the global pagemap a static field so that its name
+   * This class makes the global pagemap a typed singleton so that its name
    * includes the type mangling.  If two compilation units try to instantiate
    * two different types of pagemap then they will see two distinct pagemaps.
    * This will prevent allocating with one and freeing with the other (because
@@ -69,21 +69,14 @@ namespace snmalloc
    * having two different types.
    */
   template<typename T>
-  class GlobalPagemapTemplate
+  struct GlobalPagemapTemplate
   {
-    /**
-     * The global pagemap variable.  The name of this symbol will include the
-     * type of `T`.
-     */
-    inline static T global_pagemap;
-
-  public:
     /**
      * Returns the pagemap.
      */
     static SuperslabPagemap& pagemap()
     {
-      return global_pagemap;
+      return TypedSingleton<SuperslabPagemap>::global;
     }
   };