libtool: Link without -flat_namespace for macOS.
* m4/libtool.m4: Not setting 10.0 to MACOSX_DEPLOYMENT_TARGET when not defined. Only specify -flat_namespace to linker for specific (older) versions and hosts.
Original patch was by: Jeremy Huddleston Sequoia <jeremyhu@apple.com>
in
https://lists.gnu.org/archive/html/libtool-patches/ 2020-06/msg00001.html
- Reported-by: Aleix Conchillo Flaque
- GnuPG-bug-id: T5610
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>