bug#44605: Support MACOSX_DEPLOYMENT_TARGET=11.0

[Alex Ameen]

Hey sorry for the radio silence. libtool was without a maintainer for a 
bit, but I just adopted recently and have been working my way through 
the bug/patch lists.

Did y'all ever reach consensus about the effect of Ryan's addition?

-    10.[012],*|,*powerpc*)
+    10.[012],*|,*powerpc*-darwin[5-8]*)

Since I saw that the Macports and Homebrew folks both landed on 
identical patches I'll plan on merging that for now.

Thanks for your help on this.