I propose that Sun create an externally-visible tree of binaries in the form that the JDK makefiles expect for ALT_SLASH_JAVA. Then OpenJDK developers could copy this tree to their development machine, set ALT_SLASH_JAVA to this directory, and most of the sanity warnings would evaporate.
Of course, this may not be possible for everything that is expected to be found in ALT_SLASH_JAVA. E.g. Sun compilers probably cannot be provided this way, because of the usual requirement to have click-through licenses?! Perhaps Sun could aggregate a complete JDK development environment in one mega-tarball, protected by just one click-through license? Perhaps Sun could provide a known-to-work copy of Cygwin for JDK development. The Cygwin project itself doesn't provide historic binaries, but if you install Cygwin by first downloading everything to disk, and then installing from there, you'll have a frozen-in-time set of Cygwin binaries that you can probably legally redistribute later when they've gotten the thumbs-up from Sun JDK development engineers. Martin