When performing template argument deduction for an initializer list,

When performing template argument deduction for an initializer list,
be sure to perform the argument type adjustments in
[temp.deduct.call]p2, e.g., array decay.

And, when performing these deductions in the context of 'auto', make
sure that we're deducing the P' in std::initializer_list<P'> rather
than the whole initializer list.

Together, this makes code like

  for( auto s : {"Deferred", "New", "Open", "Review"}) { }

work properly.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@153998 91177308-0d34-0410-b5e6-96231b3b80d8