acinclude/libtool.m4: Apply macos11 patch from libtool bug #44605

https://debbugs.gnu.org/cgi/bugreport.cgi?bug=44605
https://github.com/macports/macports-ports/blob/master/devel/libtool/files/dynamic_lookup-11.patch
( Also see https://debbugs.gnu.org/cgi/bugreport.cgi?bug=44684 )

This also implicitly covers the macos10.10+ support patch from libtool
mainstream which has been in since libtool-v2.4.3, i.e.:
http://git.savannah.gnu.org/gitweb/?p=libtool.git;a=commit;h=e145288b059e14ab7e58fc6a304e82d9dad282a6
2 files changed