c++: refactor some parser code

[Nathan Sidwell]

cp_parser_declaration copies tokens to local variables, before 
inspecting (some of) their fields.  There's no need.  Just point at them 
in the token buffer -- they don't move.  Also, we never look at the 
second token if the first is EOF, so no need for some kind of dummy 
value in that case.

             gcc/cp/
             * parser.c (cp_parser_declaration): Avoid copying tokens.
             (cp_parser_block_declaration): RAII token pointer.

pushed

-- 
Nathan Sidwell
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