java-gcj-compat's original purpose was to install a collection of wrapper scripts, symlinks and jar files to provide an SDK-like interface to the GCJ tool set.
Today, most of java-gcj-compat has been merged into GNU Classpath and libgcj, where it belongs. However, java-gcj-compat still hosts some packaging scripts that don't obviously belong anywhere else: aot-compile, aot-compile-rpm and rebuild-gcj-db.