[c++-concepts]: Requires expression

[Andrew Sutton <andrew dot n dot sutton at gmail dot com>]

Attached is the stubbed out parsing for requires expressions. I plan
on implementing semantics next.

I haven't pushed this into a git branch since its a completely
separate change from the previous patch. Should I create a new branch
for separate work?

Changelog:

2013-06-21  Andrew Sutton  <andrew.n.sutton@gmail.com>
        * gcc/cp/parser.c (cp_parser_requires_clause): Pulled out of
        cp_parser_requires_clause_opt for reuse in the requires expr parser.
        (cp_parser_requires_expression): New, along with a family of
        sub-expression parsers for the new feature.
        * gcc/cp/semantics.c (finish_requires_expr): Stub.
        (finish_syntax_requirement): Stub.
        (finish_type_requirement): Stub.
        (finish_constexpr_requirement): Stub.
        (finish_noexcept_requirement): Stub.
        (finish_requires_expr): Stub.
        * gcc/cp/cp-tree.h: (finish_requires_expr): New.
        (finish_syntax_requirement): New.
        (finsih_type_requirement): New.
        (finish_constexpr_requirement): New.
        (finish_noexcept_requirement): New.

Andrew

Attachment: reqexpr-1.patch
Description: Binary data