Implement C++03 [dcl.init]p5's checking for value-initialization of references

properly, rather than faking it up by pretending that a reference member makes
the default constructor non-trivial. That leads to rejects-valids when putting
such types inside unions.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@169662 91177308-0d34-0410-b5e6-96231b3b80d8