Disabling libjava on platforms in which it won't build

[Alexandre Oliva]

People have found problems in building libjava out of the branch on
IRIX 6.*, HP-UX and Solaris 8, so I'm checking this in mainline and
branch before I lose track of the reports I got.  If you have any
reason to doubt the reports, --enable-libgcj should get libjava
configured to build, and either the problem documented in this patch
will be duplicated, it is fixed or there's something different in your
environment, which we'd like to hear about.

Mark, may I go ahead and enable the Java front-end by default now?  It
seems that the only ports that still have libgcj enabled are:

GNU/Linux (all architectures), ia64-elf, Mingw32, Cygwin, Solaris/x86
(all versions), Solaris/sparc (all versions except Solaris 8),
beos/x86, sparc-elf and sparc64-elf

I don't know if any of these are oversights (I seem to recall someone
mentioning it wouldn't build or work on Cygwin; perhaps Mingw32 is
affected similarly), but I believe it would be reasonably safe to
enable the Java front-end by default in the branch after this patch.
Do you agree?  May I go ahead and check in the patch to
gcc/java/config-lang.in to that effect?