Update to jdk-21.0.6

[Makarius]

On 24/01/2025 20:39, Makarius wrote:
> 
> An interesting side-remark in the changelog is about CRaC: https:// 
> wiki.openjdk.org/display/crac --- this will eventually provide something like 
> a "dumped heap image" as we are accustomed to in Poly/ML. Welcome back to the 
> old LISP Club, OpenJDK!

Here is some more information: 
https://docs.azul.com/core/crac/crac-introduction with a video presentation at 
the bottom.

Main conclusions:

   * works only for Linux --- primarily x86_64, but now also arm64

   * no macOS, no Windows

It is more like an old Emacs or TeX image dump, not quite the ML heap dump 
that we know of.


	Makarius