[Bug c++/87380] Explicit instantations should use weak symbols on darwin

[iains at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87380

--- Comment #11 from Iain Sandoe <iains at gcc dot gnu.org> ---
(In reply to mrs@gcc.gnu.org from comment #10)
> I've related 15428 which has some details for why this is the way it is.
> 
> Unless the underlying bug has been fixed in the linker, changing this will
> merely re-introduce the previous bug that was fixed.  If we do that, we need
> to weigh which feature we want to work and which to break.  The previous
> answer, was to make static linking work.
> 
> See 2004-06-03  Matt Austern  <austern@apple.com> and 2004-03-12  Matt
> Austern  <austern@apple.com> for the totality of the code.

Yup .. I've been looking at that.
We already have the linker version, so should be able to make an intelligent
choice.

However, as I read the original bug (against powerpc-darwin7), it might
actually be ar that's the problem - since it's the presence of weak extern
symbols in the archive TOC that's the issue.  If that's the case, I'm sure we
can run a config. test to see if ar meets the criteria.

Anyway, trying to work my way back to a cut-off point (I don't have an easy way
to test if powerpc-darwin7 will actually bootstrap any recent GCC - but suspect
that it will not without an updated as/ld at minimum).