$NetBSD$

Support tbb 2021.3 from
https://github.com/AcademySoftwareFoundation/openvdb/commit/5b0ec82307c603adb147cee4bc1a925d407141f5

--- openvdb/openvdb/CMakeLists.txt.orig	2021-06-11 21:38:41.000000000 +0000
+++ openvdb/openvdb/CMakeLists.txt
@@ -434,6 +434,7 @@ set(OPENVDB_LIBRARY_UTIL_INCLUDE_FILES
   util/NodeMasks.h
   util/NullInterrupter.h
   util/PagedArray.h
+  util/Threading.h
   util/Util.h
 )
 
