Avoid compilation error when passing in heap to allocators

Before it would not work to create the mi_heap_stl_allocator types with
passing in a "mi_heap_t*", since sizeof is used and it gives a
compilation error. This change fixes that.

include/mimalloc.h

@@ -487,6 +487,7 @@ template<class T1,class T2> bool operator!=(const mi_stl_allocator<T1>& , const
 #define MI_HAS_HEAP_STL_ALLOCATOR 1
 
 #include <memory>      // std::shared_ptr
+#include "mimalloc/types.h"
 
 // Common base class for STL allocators in a specific heap
 template<class T, bool _mi_destroy> struct _mi_heap_stl_allocator_common : public _mi_stl_allocator_common<T> {