Hi Guix,

this patch adds the GNU Compiler for Java to the gcc module.  We need
GCJ to build IcedTea6 / OpenJDK, which in turn could be used to build
IcedTea7.

GCJ unfortunately has a binary dependency, the Eclipse Compiler for
Java.  GCJ expects to be given the path of the ecj.jar at compile time.
ECJ is provided as ecj-bootstrap-4.8.  I don't know if GCJ is built such
that this ECJ binary is no longer required at the end (but I know that
IcedTea6 also needs the ECJ jar).  For IcedTea6 we could compile ECJ
from source with GCJ, but I don't know how to deal with GCJ's dependency
on ECJ.  Having it depend on a binary is ugly.

GCJ is built with options to create symlinks to function as a primitive
JDK.  It does not provide wrappers for javap and javac, so these are
added in an extra phase.  I took the javac perl wrapper from Gentoo, but
I suppose a script in Guile might be nicer (there is no official
upstream source for the wrapper script, so we might as well roll our
own).

Anyway, your comments are very welcome.

-- Ricardo