[Bug c/68868] atomic_init emits an unnecessary fence

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68868

--- Comment #3 from Martin Sebor <msebor at gcc dot gnu.org> ---
A working patch posted for review:
https://gcc.gnu.org/ml/gcc-patches/2015-12/msg01449.html