[RFA/commit 5/5] Add -Wunused-function to compile flags.

[Joel Brobecker]

> gdb/ChangeLog:
> 
>         * configure.ac: Add -Wunused-function to build_warnings.
>         * configure: Regenerate.

This patch, and all 4 patches before it, have now been checked in.
Things should be fine on GNU/Linux systems, but I suspect those of us
using more exotic systems will have to commit some extra fixes...

I'm going to resync AdaCore's sources, so you might see some extra
patches coming from AdaCore soon :)

-- 
Joel