How to know which front end?

[David Daney]

I am hacking up an optimization pass that re-writes some calls to 
libgcj.  Since this pass is only useful if the source is generating 
calls to functions in libgcj, I only want to enable it if this is likely 
to be the case.

Q: Is there some predicate that can be used in the gate of a tree 
optimizer to disable the pass if not being called via the java front-end?

Thanks,
David Daney