[Bug c++/95428] New: ABI breakage for "base object constructor" for final classes

[P at draigBrady dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95428

            Bug ID: 95428
           Summary: ABI breakage for "base object constructor" for final
                    classes
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: P at draigBrady dot com
  Target Milestone: ---

The change to elide the "base object constructor" for final classes in bug
#70462 introduces an ABI incompatibility with clang 9 at least.

I'm seeing this with kuduraft-1.8 compiled with GCC 10, giving linker errors
from clang 9.0.20190721 like:

  error: undefined symbol: kudu::consensus::OpId::OpId()

Reverting the change in #70462 fixes the issue