initial patch to install libiberty headers

[DJ Delorie]

> DJ, would there be any serious gotchas in converting libiberty to use
> automake?  Just to keep the option open?

I don't know of any *serious* gotchas, but be aware that libiberty is
one of the few packages built *twice* in each "monolithic" build -
once for the host, and once for the target.  Any patches affecting the
configury would need to be extensively tested before being applied.
This includes binutils/gdb/cygwin testing.

Libiberty is also a very old package, and may have history I'm not
aware of.