[Patch] Fix undefined behaviors in regex

[Tim Shen]

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 :)

Thanks!


-- 
Tim Shen

a.patch
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