Add fix to support Summon/Linaro GCC ARM embedded toolchain.

Hi, would you please to review and merge it? Without this fix it produces unresolved _exit reference on ld stage due to omitted nosys library. It happens because summon/linaro gcc reports a different signature on 'gcc --version'. So gcc still unrecognized by build system. Tested with:

arm-none-eabi-gcc (Linaro GCC 4.6-2011.10) 4.6.2 20111004 (prerelease)
Copyright (C) 2011 Free Software Foundation, Inc.

Thank you,
Dmitry