See http://reviews.gem5.org/r/831/

This patch enables compiling the Java JNI for gem5Ops for the X86 target.

As with the ARM target, the JNI libraries won't build by default. The change to CFLAGS might cause some problems on a system without Java, and the user should still set the JDK_PATH, so perhaps it should be unset like in Makefile.arm.

I also overrode / got rid of the -DM5OP_ADDR which might not be desirable.

I built and ran an example similar to the one on the wiki (Hello World with rpns).