Fix handling of braced-init-list as reference initializer within
aggregate initialization. Previously we would incorrectly require an
extra set of braces around such initializers.
Pull in r188718 from upstream clang trunk:
Handle init lists and _Atomic fields.
Fixes PR16931.
These fixes are needed for the atomic_flag type to work correctly in our
stdatomic.h.
Requested by: theraven
992b133da5