PR20844: If we fail to list-initialize a reference, map to the referenced type
before retrying the initialization to produce diagnostics. Otherwise, we may
fail to produce any diagnostics, and silently produce invalid AST in a -Asserts
build. Also add a note to this codepath to make it more clear why we were
trying to create a temporary.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@217197 91177308-0d34-0410-b5e6-96231b3b80d8