[Patch] Fix undefined behaviors in regex

[Paolo Carlini]

On 10/16/2013 11:48 PM, Tim Shen wrote:
> It's detected by `clang++ -g -std=c++11 -fsanitize=undefined` but not
> detected by g++ with flags `g++ -g -std=c++11 -fsanitize=undefined
> -lpthread`. Am I on the right way?
>
> -m32 and -m64 tested :)
Thank you!

Paolo.