[Bug c++/84497] link errors with trivial external thread_local variables

[nathan at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84497

--- Comment #3 from Nathan Sidwell <nathan at gcc dot gnu.org> ---
Created attachment 43550
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43550&action=edit
Simpler testcase

The simpler testcase removes all the atomic cruft. Compile with -DDEF to get
the defining object file and without that define to get the using object file.

for the base type:
  TYPE_NEEDS_CONSTRUCTING      true
  TYPE_HAS_CONSTEXPR_CTOR      true
  TYPE_HAS_TRIVIAL_DESTRUCTOR  true
  DECL_EXTERNAL                true

for the derived type:
  TYPE_NEEDS_CONSTRUCTING      true
  TYPE_HAS_CONSTEXPR_CTOR      false
  TYPE_HAS_TRIVIAL_DESTRUCTOR  true
  DECL_EXTERNAL                true