PR13273: When performing list-initialization with an empty initializer list,

PR13273: When performing list-initialization with an empty initializer list,
actually perform value initialization rather than trying to fake it with a call
to the default constructor. Fixes various bugs related to the previously-missing
zero-initialization in this case.

I've also moved this and the other list initialization 'special case' from
TryConstructorInitialization into TryListInitialization where they belong.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@159733 91177308-0d34-0410-b5e6-96231b3b80d8