toolchain/gcc (linaro): fix extension elimination optimization

This applies Richard Sandiford's patch for Linaro GCC as an alternative to disabling the Linaro-specific extension elimination optimization altogether.

Original patch: https://bugs.launchpad.net/gcc-linaro/+bug/728315


Signed-off-by: Mark Mentovai <mark@moxienet.com>

SVN-Revision: 25871