Let -for_backup perform -lfa_flags only if enabled at compile time in libisofs

xorriso/xorriso.texi

@@ -50,7 +50,7 @@
 @c man .\" First parameter, NAME, should be all caps
 @c man .\" Second parameter, SECTION, should be 1-8, maybe w/ subsection
 @c man .\" other parameters are allowed: see man(7), man(1)
-@c man .TH XORRISO 1 "Version 1.5.7, Jul 21, 2024"
+@c man .TH XORRISO 1 "Version 1.5.7, Jul 23, 2024"
 @c man .\" Please adjust this date whenever revising the manpage.
 @c man .\"
 @c man .\" Some roff macros, for reference:
@@ -1403,6 +1403,9 @@ Enable all extra features which help to produce or to restore backups with
 highest fidelity of file properties. Currently this is a shortcut for:
 @*
   -hardlinks on -acl on -xattr any -md5 on 
+@*
+and possibly:
+@*
   -lfa_flags default:on:restore_mask=aAcCdDijmPsStTux
 @*
 If you restore a backup with xattr from non-user namespaces, then make sure
@@ -1416,10 +1419,14 @@ events.
 Command -xattr "user" after command -for_backup will exclude non-user
 attributes from being recorded or restored.
 @*
-The -lfa_flags restore mask of -for_backup enables all known settable
-attributes, except "F" which has special constraints which xorriso cannot yet
-detect at restore time. Command -lfa_flags "restore_mask=" after -for_backup
-will enable all known settable attributes.
+The command -lfa_flags is executed by -for_backup only if the underlying
+libisofs was compiled with support for Linux file attributes,
+which is typically not the case on non-Linux systems.
+@*
+If -lfa_flags is executed by -for_backup then the restore mask enables all
+known settable attributes, except "F" which has special constraints which
+xorriso cannot yet detect at restore time. Command -lfa_flags "restore_mask="
+after -for_backup will enable all known settable attributes.
 @c man .TP
 @item -ecma119_map "stripped"|"unmapped"|"lowercase"|"uppercase"
 @kindex -ecma119_map    names w/o Rock Ridge, Joliet