[PATCH] Fix regex_iterator end() state and operator==()

[Tim Shen]

This fixes libstdc++/78236. I'm surprised that this bug was not
revealed until now :P.

Bootstrapped and tested under x86_64-linux-gnu.

I'm happy with however many backports.

-- 
Regards,
Tim Shen
-------------- next part --------------
A non-text attachment was scrubbed...
Name: a.diff
Type: text/x-patch
Size: 3149 bytes
Desc: not available
URL: <http://gcc.gnu.org/pipermail/libstdc++/attachments/20161108/2338a51c/attachment.bin>