avcodec/x86/cabac: factorize broken llvm/clang check out

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/x86/cabac: Disable get_cabac_bypass_x86() on broken llvm/clang

This should fix fate on these platforms

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