Suggest fix-it ':' when '=' used in for-range-declaration

Fix for PR19176. Clang will suggest a fix-it hint for cases like:
  int arr[] = {1, 2, 3, 4};
  for (auto i = arr)
              ^
              :


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@208299 91177308-0d34-0410-b5e6-96231b3b80d8