gen.pl: change wording for mutexed options

Instead of saying "This option overrides NNN", now say "This option is
mutually exclusive to NNN" in the generated man page ouput, as the
option does not in all cases actually override the others but they are
always mutually exclusive.

Ref: #8704
Closes #8716

docs/cmdline-opts/gen.pl

@@ -349,7 +349,8 @@ sub single {
             my $l = manpageify($k);
             $mstr .= sprintf "%s$l", $mstr?" and ":"";
         }
-        push @foot, overrides($standalone, "This option overrides $mstr. ");
+        push @foot, overrides($standalone,
+                              "This option is mutually exclusive to $mstr. ");
     }
     if($examples[0]) {
         my $s ="";