Add an UNDEFINED_VERSION option

[brooks]

Summary

When enabled (current default) link with --undefined-version to allow
symbol maps to contain symbols not defined by libraries. When disabled,
link with --no-undefined-version to disallow these bugs.

WITHOUT_UNDEFINED_VERSION is currently broken. Once it is fixed it
should be made the default and this option should likely be removed.

[dim]

Is this meant as a transitional tool? Or do we expect to have some sub-Makefiles still set MK_UNDEFINED_VERSION=no because they cannot be fixed?

[brooks]

I'd like it to be a transitional tool.

[brooks]

I've got a set of patches for libc that I'll be posting for review, mostly deleting bogus entries.

[emaste]

share/mk/bsd.lib.mk

263–268

Do all lld and bfd versions of interest support both options? I.e., could we just always pass one or the other?

[brooks]

share/mk/bsd.lib.mk

263–268

Recent bfd linkers support these options. It could be that we could ignore the default value and always pass one.

[brooks]

Drop lld version conditionals and just add the flags

[dim]

Sure, then I'm totally fine with this. It's better to incrementally fix the problems and then remove this option. Preferably before stable/15 gets branched :)