Fix build on ocaml-4.00.1

Signed-off-by: Jon Ludlam <jonathan.ludlam@citrix.com>
Merge pull request #1850 from jonludlam/ocaml-4.00.1-build-fix

Fix build on ocaml-4.00.1
CP-8888: Add diagnostic stats reporting

Signed-off-by: John Else <john.else@citrix.com>