During a test rebuild of ecj-2.1.3-5 in the mock builder, the following
problem manifests itself:

+ find -name '*.class' -or -name '*.properties' -or -name '*.rsc'
+ xargs jar cf ../../../ecj-2.1.3.jar
xargs: jar: No such file or directory
error: Bad exit status from /var/tmp/rpm-tmp.45084 (%build)

The reason is, that the Required libgcj installs fastjar, but doesn't set up the
correct symlink with the alternatives system.
This is done by the java-$ver-compat package, which is not being installed.

According to nasrat the best way of dealing with this issue is dropping the
BuildRequires for gcc-java and libgcj and just setting a BuildRequire for
java-$ver-compat, or even better the virtual java-devel package which is
provided by the java-compat package. This will fix the alternatives problem and
pull in gcj and libgcj as well.

This bug is at least present in RHEL4, FC4, FC3 and current RawHide. Bugs were
filed for these releases as well.