Implement DR136

Friend declarations that specify a default argument must be a definition
and the only declaration in the translation unit.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@184889 91177308-0d34-0410-b5e6-96231b3b80d8
Don't check for triviality on fields of templated records. We can't know the
answer until after instantiation. Fixes PR16061!


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@184890 91177308-0d34-0410-b5e6-96231b3b80d8