added missing file (cf. 124432e77ecf);

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Pure/ML-Systems/polyml-5.5.2.ML	Thu Dec 12 16:25:21 2013 +0100
@@ -0,0 +1,23 @@
+(*  Title:      Pure/ML-Systems/polyml-5.5.2.ML
+    Author:     Makarius
+
+Compatibility wrapper for Poly/ML 5.5.2.
+*)
+
+structure Thread =
+struct
+  open Thread;
+
+  structure Thread =
+  struct
+    open Thread;
+
+    fun numProcessors () =
+      (case Thread.numPhysicalProcessors () of
+        SOME n => n
+      | NONE => Thread.numProcessors ());
+  end;
+end;
+
+use "ML-Systems/polyml.ML";
+