Add the TypeSourceInfo for the lambda call operator to the lambda's

Add the TypeSourceInfo for the lambda call operator to the lambda's
definition info; it needs to be there because the mangler needs to
access it before we're finished defining the lambda class.
PR12808.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@164186 91177308-0d34-0410-b5e6-96231b3b80d8