make check errors on recent MacOS versions appear to be due to new default linker in XCode

[Marc Glisse]

On Wed, 2 Oct 2024, Mark Mentovai wrote:

> https://git.savannah.gnu.org/cgit/libtool.git/commit/m4/libtool.m4?id=9e8c882517082fe5755f2524d23efb02f1522490,
> in libtool-2.4.7, modernizes this check in libtool, and with that in use,
> does not enable -flat_namespace in this situation. Upgrading libtool in gmp
> to that version will fix this problem.

https://gmplib.org/list-archives/gmp-bugs/2023-August/005355.html
This has been done a while ago, and can be seen in snapshots from 
https://gmplib.org/download/snapshot/gmp-next/, but there hasn't been a 
release since then.

-- 
Marc Glisse