avcodec/x86/cabac: include get_cabac_bypass_sign_x86() under #if !BROKEN_COMPILER

this might fix Ticket2999 as well as some fate clients
untested as the original patch submitter no longer has the environment to test
this should be reverted if it does not fix the issues

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>