More -Wuninitialized updates

Fix r216438 to catch more complicated self-initialized in std::move.  For
instance, "Foo f = std::move(cond ? OtherFoo : (UNUSED_VALUE, f));"

Make sure that BinaryConditionalOperator, ConditionalOperator, BinaryOperator
with comma operator, and OpaqueValueExpr perform the correct usage forwarding
across the three uninitialized value checkers.