stap libdwfl bug-compatibility requirements

[Frank Ch. Eigler]

Roland McGrath <roland@redhat.com> writes:

> We are preparing to release version 0.138 of elfutils.  I gather that
> systemtap might be expecting some buggy old behavior that we've fixed.
> [...]
> I don't propose to worry about preexisting systemtap sources being
> freshly rebuilt against elfutils-devel >= 0.138.

As discussed on IRC, I suggest we do worry about this case.  One
possible solution is to give the bug-fixed variant a new name and
preserve the old one (perhaps only as hidden implementation exposed
via symbol versioning):

old/deprecated: dwfl_module_build_id
new/fixed:      dwfl_module_build_id_bits

Systemtap does not use the other build-id-related functions, and this
may have been the only one affected by the bug.

- FChE