NEWS: update to polyml-5.9.2

[Makarius]

*** System ***

* Update to official Poly/ML 5.9.2, with minor changes to word and
floating-point arithmetic.


This refers to Isabelle/a356fd7ca1c4 where the polyml component now includes 
Intel macOS executables.

Moreover, in Isabelle/08722f90a439 I have a recent test on word arithmethic by 
Florian Haftmann: "discontinue obsolete test from d4eaefc626ec: max_index is 
the largest possible word".


	Makarius