AFAICT, with the changes I committed yesterday, weak symbols work at
least as well as the `indirect symbol' hack does with a.out.  I can't
find any symbols that are actually missing from the library, and the
system builds and appears to work with weak symbols in place.

Also, using them fixes a problem I'm having with third party software
that includes its own DB library.

So, unless there is something actually *broken* when weak symbols are
enabled, I plan to remove __DO_NOT_DO_WEAK__ very soon.