Require boundaries around local labels in handle_local_label

Since we're doing a replace of a string that looks like e.g "1b"
over a full line, such a string could concievably be a substring of
another identifier as well.

This doesn't fix any known issue, but attempts to make this
less fragile.

Author: mstorsjo

gas-preprocessor.pl

@@ -631,12 +631,12 @@ sub handle_local_label {
     my $dir  = $_[2];
     my $target = "$num$dir";
     if ($dir eq "b") {
-        $line =~ s/$target/$last_temp_labels{$num}/g;
+        $line =~ s/\b$target\b/$last_temp_labels{$num}/g;
     } else {
         my $name = "temp_label_$temp_label_next";
         $temp_label_next++;
         push(@{$next_temp_labels{$num}}, $name);
-        $line =~ s/$target/$name/g;
+        $line =~ s/\b$target\b/$name/g;
     }
     return $line;
 }