For "expected unqualified-id" errors after a double colon, and the double colon

For "expected unqualified-id" errors after a double colon, and the double colon
is at the end of the line, point to the location after the double colon instead
of at the next token.  There is more context to be given this way.  In addition,
the next token can be several lines later.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190029 91177308-0d34-0410-b5e6-96231b3b80d8