Suppress lld 16 errors about undefined symbols in version maps

lld >= 16 turned on --no-undefined-version by default, which results in
errors whenever symbols are mentioned in version maps, but are not
actually defined in the binary.

Since we have quite a few instances of symbols that are defined or not,
depending on various compile-time settings, suppress this lld check for
the time being.

MFC after: 1 week