[Bug libstdc++/79980] Possible bug in codecvt.cpp bitmask setting code

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79980

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Patch posted to https://gcc.gnu.org/ml/gcc-patches/2017-03/msg00675.html

Will be committed for stage 1