Combined toolchain build

[DJ Delorie]

In general, you should avoid doing a combined tree using released
branches of packages.  The combined tree is best when you're working
with the current development branches, because the common parts will
then be in sync.

If you're building released packages, it's best to build them in
separate trees, because of the problems you mention.  However, in the
case of libiberty, it's often possible to simply use whichever
libiberty seems newer, or in some cases, just use the development
version of libiberty and include from the binutils project (binutils'
include has more files than gcc's).