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

acinclude/libtool.m4

@@ -1047,16 +1047,11 @@ _LT_EOF
       _lt_dar_allow_undefined='${wl}-undefined ${wl}suppress' ;;
     darwin1.*)
       _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-    darwin*) # darwin 5.x on
-      # if running on 10.5 or later, the deployment target defaults
-      # to the OS version, if on x86, and 10.4, the deployment
-      # target defaults to 10.4. Don't you love it?
-      case ${MACOSX_DEPLOYMENT_TARGET-10.0},$host in
-	10.0,*86*-darwin8*|10.0,*-darwin[[91]]*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
-	10.[[012]]*)
+    darwin*)
+      case $MACOSX_DEPLOYMENT_TARGET,$host in
+	10.[[012]],*|,*powerpc*-darwin[[5-8]]*)
 	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-	10.*)
+	*)
 	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
       esac
     ;;

configure

@@ -6924,16 +6924,11 @@ $as_echo "$lt_cv_ld_force_load" >&6; }
       _lt_dar_allow_undefined='${wl}-undefined ${wl}suppress' ;;
     darwin1.*)
       _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-    darwin*) # darwin 5.x on
-      # if running on 10.5 or later, the deployment target defaults
-      # to the OS version, if on x86, and 10.4, the deployment
-      # target defaults to 10.4. Don't you love it?
-      case ${MACOSX_DEPLOYMENT_TARGET-10.0},$host in
-	10.0,*86*-darwin8*|10.0,*-darwin[91]*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
-	10.[012]*)
+    darwin*)
+      case $MACOSX_DEPLOYMENT_TARGET,$host in
+	10.[012],*|,*powerpc*-darwin[5-8]*)
 	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-	10.*)
+	*)
 	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
       esac
     ;;