When building with Tycho, I get:
[ERROR] Failed to execute goal org.eclipse.tycho:tycho-compiler-plugin:0.14.0-SNAPSHOT:compile (default-compile) on project org.jboss.tools.forge.runtime.ext: Compilation failure: Compilation failure:
[ERROR] /home/mistria/workspaceJBossTools/trunk/forge/plugins/org.jboss.tools.forge.runtime.ext/src/org/jboss/tools/forge/runtime/ext/CtrlCAction.java:[8,0]
[ERROR] import sun.misc.Signal;
[ERROR] ^^^^^^^^^^^^^^^
[ERROR] Access restriction: The type Signal is not accessible due to restriction on classpath entry /usr/lib/jvm/java-6-openjdk/jre/lib/rt.jar

To be clear with OSGi, the forge component has to provide a "framework extension bundle" to re-export these libs: see http://blog.meschberger.ch/2008/10/osgi-bundles-require-classes-from.html