Every once in a while people want to be analyze C code. If you are one of those people, checkout bug 494960. For GCC 4.3, you’ll need to update your patch queue. If you you followed the Dehydra install instructions do something like:
hg pull -u
hg qpush -a
and rebuild gcc to get C support in the plugin framework for GCC 4.5 (patch for trunk is in the bug).
Everything other than process_function should work in both treehydra and dehydra. Note that the objects provided by GCC will be slightly different in structure due to the underlying difference between gcc/g++, so scripts that were written for C++ may need to be updated.