Change GCC spec to support upgraded binutils

New version of binutils have three regimes: --32, --64 and default
(which is not identical to --64 !!!).

Force --64 if x86_64 mode is used.

Also -m options for ld are changed.

R=mcgrathr@chromium.org

Review URL: https://codereview.chromium.org/23567025
1 file changed