When parsing an identifier as an expression in C++, only try to annotate it

When parsing an identifier as an expression in C++, only try to annotate it
as a type or scope token if the next token requires it.

This eliminates a lot of redundant lookups in C++, but there's room for
improvement;  a better solution would do a single lookup whose kind and
results would be passed through the parser.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@92930 91177308-0d34-0410-b5e6-96231b3b80d8