Fix #631 (#633)

* Fix #631

Add wrapper override for the Windows variant of maloc_usable_size : _msize

Co-authored-by: Matthew Parkinson <mjp41@users.noreply.github.com>

src/snmalloc/override/malloc.cc

@@ -41,6 +41,14 @@ extern "C"
     return snmalloc::libc::malloc_usable_size(ptr);
   }
 
+#ifdef _WIN32
+  SNMALLOC_EXPORT
+  size_t SNMALLOC_NAME_MANGLE(_msize)(MALLOC_USABLE_SIZE_QUALIFIER void* ptr)
+  {
+    return snmalloc::libc::malloc_usable_size(ptr);
+  }
+#endif
+
   SNMALLOC_EXPORT
   size_t SNMALLOC_NAME_MANGLE(malloc_good_size)(size_t size)
   {