gnu: Add ocaml-mirage-clock.

* gnu/packages/ocaml.scm (ocaml-mirage-clock): New variable.

Signed-off-by: Christopher Baines <mail@cbaines.net>

gnu/packages/ocaml.scm

@@ -3825,6 +3825,30 @@ (define-public ocaml-mirage-time
      "Defines the signature for time-related operations for MirageOS.")
     (license license:isc)))
 
+(define-public ocaml-mirage-clock
+  (package
+    (name "ocaml-mirage-clock")
+    (version "4.2.0")
+    (source (origin
+              (method git-fetch)
+              (uri (git-reference
+                    (url "https://github.com/mirage/mirage-clock")
+                    (commit (string-append "v" version))))
+              (file-name (git-file-name name version))
+              (sha256
+               (base32
+                "0rkara9i3dvnzrb8jl2vkx8hgamvxnksin67wmhbv9d4i758amjy"))))
+    (build-system dune-build-system)
+    (home-page "https://github.com/mirage/mirage-clock")
+    (synopsis "Libraries and module types for portable clocks")
+    (description
+     "This library implements portable support for an operating system
+timesource that is compatible with the MirageOS library interfaces.  It
+implements an @code{MCLOCK} module that represents a monotonic timesource
+since an arbitrary point, and @code{PCLOCK} which counts time since the Unix
+epoch.")
+    (license license:isc)))
+
 (define-public ocaml-mirage-unix
   (package
     (name "ocaml-mirage-unix")