"This configuration is not supported ..."

[Joe Buck]

When I configure the current CVS code on a Red Hat 6.2 box, I get ...

Configuring for a i686-pc-linux-gnu host.
*** This configuration is not supported in the following subdirectories:
     target-libffi target-boehm-gc target-zlib target-libjava target-libchill
    (Any other directories should still work fine.)

However, the compiler bootstraps OK.  Why these messages, and what is
missing?