dredge through old files

- top-level: make an OpenSourceLicenses directory and copy gdb.txt
there, to clarify what it is
- rename "darwinbuild" directory to "darwinbuild-OpenSourceVersions"
- un-obsolete and touch a bunch of old code files that had not been
modified in over a decade
- add some configure checks to try to help with compiling really old
Classic MacOS files (trying to compile those files still fails, so I
have kept them out of the Makefile)
- add a rule to compile regex.o in libiberty's Makefile
- re-break the test suite (oops)

Change-Id: I924bb4c4c2d48f71015e8a5adc08dc858f050a1c