macOS: use -macos_version_min for recent versions

-macosx_version_min was renamed. Ideally we would base this on the version of
the toolset used, but we don't know that. Instead, use it when targeting
more recent macOS versions

compiler/systems/t_darwin.pas

@@ -354,7 +354,12 @@ implementation
       begin
         if MacOSXVersionMin.isvalid then
           begin
-            result:='-macosx_version_min '+MacOSXVersionMin.str;
+           { This does not depend on the target version but on the toolchain
+             version, but we only know the former and not the latter }
+           if MacOSXVersionMin.relationto(11,0,0)>=0 then
+             result:='-macosx_version_min '+MacOSXVersionMin.str
+           else
+             result:='-macos_version_min '+MacOSXVersionMin.str;
           end
         else if iPhoneOSVersionMin.isvalid then
           begin