cc/gcc: do not build plugins for static toolchains

Plugins are shared objects, and when building a toolchain statically,
the gcc build system breaks havok (although there is no hard technical
reasons it should not be possible)...

And consequently, do not enable plugin supoprt in binutils.

Reported-by: Thomas Spurden <thomas@ado.is-a-geek.net>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

reporter_name="Harold Grovesteen"

reporter_url="http://sourceware.org/ml/crossgcc/2009-11/msg00052.html"

reporter_comment=""