Build environment for the NSO Classic builds of FreeJ2ME-Plus.

This file is a convenience for anyone who wants to rebuild a release and
compare the result against the archive we published. It is not part of the
Corresponding Source: GPLv3 section 1 excludes general-purpose tools used
unmodified, so the JDK and Ant are not something the licence obliges us to
ship or to name. The source tarball plus its build file already satisfy
section 6 on their own.

Why name them anyway: `javac` output is version-dependent. The same commit
compiled with OpenJDK 26.0.2 produced 115 of 1295 class files with bytes
different from the OpenJDK 17.0.18 build -- no source difference involved.
Without knowing which compiler produced the published archive, a digest
comparison fails for reasons that say nothing about the code, so the check
is only worth running with a matching toolchain.

Archive timestamps are pinned separately, by `jar.modificationtime` in
`build.xml`. That makes repeated builds on one machine byte-identical. It
does not make builds across toolchains identical, and nothing here claims a
reproducible build in the strict sense: that would need independent clean
builds compared across machines, which has not been done.

  release        toolchain                                notes
  -------------  ---------------------------------------  ----------------------
  1.52-nso.5     OpenJDK 17.0.18, Apache Ant 1.10.17      packed with wall-clock
                                                          timestamps; the
                                                          published archives
                                                          predate both this
                                                          file and
                                                          `jar.modificationtime`,
                                                          so compare content
                                                          per entry rather than
                                                          whole-JAR digests
  1.52-nso.6     OpenJDK 17.0.18, Apache Ant 1.10.17      first release packed
                                                          with a pinned
                                                          `jar.modificationtime`,
                                                          so a rebuild on this
                                                          toolchain reproduces
                                                          the published digests
  1.52-nso.7     OpenJDK 17.0.18, Apache Ant 1.10.17      built but never
                                                          published: the CDN
                                                          key was requested
                                                          before the upload,
                                                          and the 404 that
                                                          answered is cached
                                                          for four hours with
                                                          no purge credential
                                                          on hand. Upload
                                                          first, probe second.
  1.52-nso.8     OpenJDK 17.0.18, Apache Ant 1.10.17      same toolchain and
                                                          pinned entry
                                                          timestamp as
                                                          1.52-nso.6

Update this table in the same commit that bumps `Released as:` in
NSO-CHANGES.txt and `jar.modificationtime` in build.xml.
