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>
(transplanted from 9139319423fd7d71017dfc974d3a06ab79e08fb8)

# AVR32 specific configuration file

config ARCH_avr32

    select ARCH_SUPPORTS_32

    select ARCH_DEFAULT_32

    select ARCH_USE_MMU

    select ARCH_DEFAULT_BE

    select ARCH_SUPPORT_ARCH

    select ARCH_SUPPORT_CPU

    select ARCH_SUPPORT_TUNE

    select ARCH_SUPPORT_FPU

     help

      The AVR32 architecture, as defined by:

        http://www.atmel.com/products/avr32