fix -Werror regressions with gcc 4.8 on x86_64

[Richard Henderson]

On 01/07/2015 03:19 PM, Roland McGrath wrote:
>> For use within glibc itself, I think we should redefine assert with NDEBUG to
>> use __builtin_unreachable.
> 
> The point of NDEBUG is to optimize out the tests, not just to avoid the
> file name, line number, and expression source strings.
> 

The tests themselves can sometimes give information to the compiler.  Showing
it that certain paths are unreachable imply information for the other paths.
The __builtin_unreachable function doesn't imply any actual effect; the paths
leading to this function should be removed.


r~