Since the default jdk changed to jdk19, DataExplorer fails at startup:
```console
$ ./result/bin/DataExplorer
java.lang.NullPointerException: Cannot read field "width" because the return value of "gde.config.Settings.getWindow()" is null
at gde.ui.DataExplorer.execute(DataExplorer.java:406)
at gde.GDE.main(GDE.java:544)
```
Therefore, pin to jdk17, which is also the latest recommended version by
upstream:
> The only requirement is the installation of a Java run-time of version
> 8 to Java 17 for the 32 bit versions and Java 11 to 17 for the 64 bit
> versions, such as IcedTea or open JDK.
https://www.nongnu.org/dataexplorer/index.html#Introduction
In v3.7.1, the `file.encoding=UTF-8` setting has been moved into the
application itself. It is not needed any more to pass it via the `java`
command line.
The program builds incorrectly for non-x86_64-linux platforms, although
they should be supported. Until the issue is understood and can be
fixed, declare support for only the x86_64-linux platform.
