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

xorriso/xorrisofs.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 XORRISOFS 1 "Version 1.5.7, Jul 21, 2024"
+@c man .TH XORRISOFS 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:
@@ -68,7 +68,7 @@
 @copying
 xorrisofs -  Emulation of ISO 9660 program mkisofs by program xorriso
 
-Copyright @copyright{} 2011 - 2023 Thomas Schmitt
+Copyright @copyright{} 2011 - 2024 Thomas Schmitt
 
 @quotation
 Permission is granted to distribute this text freely.
@@ -943,7 +943,7 @@ Alias of -rr_reloc_dir "/.rr_moved"
 Enable all options which improve backup fidelity:
 @*
 @minus{}@minus{}acl, @minus{}@minus{}xattr-any, @minus{}@minus{}md5,
-@minus{}@minus{}hardlinks, @minus{}@minus{}lfa_flags. 
+@minus{}@minus{}hardlinks, and possibly @minus{}@minus{}lfa_flags. 
 @*
 If you later restore a backup with xattr from non-user namespaces, then make
 sure that the target operating system and filesystem know what these attributes
@@ -953,6 +953,10 @@ privileges and just record what is readable.
 @*
 Option @minus{}@minus{}xattr after option @minus{}@minus{}for_backup excludes
 non-user attributes from being recorded.
+@*
+Option @minus{}@minus{}for_backup enables @minus{}@minus{}lfa_flags only if
+the underlying libisofs was compiled with support for Linux file attributes,
+which is typically not the case on non-Linux systems.
 @c man .TP
 @item @minus{}@minus{}acl
 @kindex @minus{}@minus{}acl   Recording of ACLs