Branch created for inter-compilation-unit references

[Michael Elizabeth Chastain]

> Michael, if you have the chance, I would appreciate it if you could run
> it through your test harness.

Okay, I'll add this branch to the next spin.  Results in about 72 hours.

> If you're really feeling adventurous, you can test the new code when
> using DWARF-2 and GCC 3.3-branch, 3.4-branch, HEAD, tree-ssa, et
> cetera: just add "--target_board unix/-feliminate-dwarf2-dups" to
> RUNTESTFLAGS.  HEAD GDB will choke on this, the branch does not in my
> testing.

I can do a special spin with -feliminate-dwarf2-dups.

> Merging the branch may have to wait until after GDB 6.1.

This process is looking like gcc, which is probably an improvement.
Develop on the branch; verify no regressions; then merge.

Michael C