Hello maintainers,

I noticed that when MACOSX_DEPLOYMENT_TARGET=11.0 is set "-Wl,-undefined"
flag is not set
because of a check in m4/libtool/m4 at
http://git.savannah.gnu.org/cgit/libtool.git/tree/m4/libtool.m4?id=b9b44533fbf7c7752ffd255c3d09cc360e24183b#n1074
that only checks for 10.*. A fix would be to check for both 10.* and 11.*

I can send a patch if you prefer.

Isuru