Fix non-working stunt ld with GCC 4.9 on Debian

With (at least) GCC 4.9 on Debian jessie the GCC spec files have changed to always use -plugin / -plugin-opt and load the LTO plugin, even if -flto is not specified to GCC.

This breaks stunt ld which does not understand these options.

I can't find _any_ documentation whatsoever on when this was enabled, and whether or not -plugin is used for anything else besides LTO support. This may also be a distro and/or upstream bug?

In any case, dropping these options should do no harm and makes app-tools work with this GCC.