In #jboss-as7 today someone reported that the current tree doesn't compile under IcedTea on Fedora.  His java version info is:

<jwulf> java version "1.6.0_18"
java version "1.6.0_18"
OpenJDK Runtime Environment (IcedTea6 1.8.1) (fedora-42.b18.fc13-x86_64)
OpenJDK 64-Bit Server VM (build 14.0-b16, mixed mode)

The errors are reported at various places where generic types with wildcards are cast to more specific types (the message is "inconvertible types".  For now I'm just recommending that you use the Sun JDK to compile on Linux, until and unless we can reproduce this error reliably and get a bug report in against IcedTea.