Hi Guix!

Here are a few patches to include the OpenJDK 15 and 16 releases, and
update 13 and 14. The codebase seems to have now moved to git, using
github as the default place to get the code.

Regarding release versions, it seems the scheme was changed for versions
10 and later to $FEATURE.$INTERIM.$UPDATE, where $INTERIM is always
zero, quoting from [0]:

--8<---------------cut here---------------start------------->8---
Under the six-month release model the elements of version numbers vary
as follows:

    $FEATURE is incremented every six months: The March 2018 release is
    JDK 10, the September 2018 release is JDK 11, and so forth.

    $INTERIM is always zero, since the six-month model does not include
    interim releases. We reserve it here for flexibility, so that a
    future revision to the release model could include such releases and
    say that JDK $N.1 and JDK $N.2 are compatible upgrades of JDK $N. As
    examples, the JDK 1.4.1 and 1.4.2 releases were, in essence, interim
    releases, and would have been numbered 4.1 and 4.2 under this
    scheme.

    $UPDATE is incremented one month after $FEATURE is incremented, and
    every three months thereafter: The April 2018 release is JDK 10.0.1,
    the July release is JDK 10.0.2, and so forth.
--8<---------------cut here---------------end--------------->8---

It seems the easiest thing to do is to refer to "GA" releases, for
"general availability" with git tags that look like "jdk-<version>-ga".

I've done it for OpenJDK 13 and later, however if we change 10, 11 and
12, it looks like a downgrade, is that a problem? 

Thanks,
Pierre

[0]: https://openjdk.java.net/jeps/322