[Patch] Fix warnings in regex

[Tim Shen]

...to prevent potential bugs.

By the way, I execute `g++ -E file.cc > prep.cc && sed -i 's|^#.*$||'
prep.cc && g++ -Wall prep.cc 2> log` to get all warnings. Do we have a
better way?

Bootstraps and tested under -m64 and -m32.

Thanks!


-- 
Tim Shen
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