[Bug target/97865] New: MACOSX_DEPLOY_TARGET needs to be updated

[juergen.reuter at desy dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97865

            Bug ID: 97865
           Summary: MACOSX_DEPLOY_TARGET needs to be updated
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: juergen.reuter at desy dot de
  Target Milestone: ---

libtool and configure do not correctly cover macOS Big Sur as the Darwin
version now reached 20 and the MACOSX_DEPLOYMENT_TARGET 11.x instead of 10.x.
All configure's need to be updated for the dynamic linking:
e.g. for libtool.m4
$ git diff
diff --git a/m4/libtool.m4 b/m4/libtool.m4
index f2d1f398..be9d50f3 100644
--- a/m4/libtool.m4
+++ b/m4/libtool.m4
@@ -1072,11 +1072,11 @@ _LT_EOF
       # 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]]*)
+    10.0,*86*-darwin8*|10.0,*-darwin[[912]]*)
       _lt_dar_allow_undefined='$wl-undefined ${wl}dynamic_lookup' ;;
     10.[[012]][[,.]]*)
       _lt_dar_allow_undefined='$wl-flat_namespace $wl-undefined ${wl}suppress'
;;
-    10.*)
+    10.*|11.*)
       _lt_dar_allow_undefined='$wl-undefined ${wl}dynamic_lookup' ;;
       esac
     ;;

etc. This then turns into configure. Without this gcc, gfortran and the dynamic
libraries get built wiht -flat_namespace instead of dynamic_lookup.