re PR c++/63455 (decltype of statement expression  internal compiler error: in cp_parser_abort_tentative_parse, at cp/parser.c:25062)

	PR c++/63455
c-family/
	* c-common.h (CPP_PREPARSED_EXPR): New.
	(N_CP_TTYPES): Adjust.
cp/
	* parser.c (struct saved_token_sentinel): New.
	(cp_parser_statement): Use it.
	(cp_parser_start_tentative_firewall): New.
	(cp_parser_end_tentative_firewall): New.
	(cp_parser_lambda_expression): Use them.
	(cp_parser_statement_expr): New.
	(cp_parser_primary_expression): Use it.

From-SVN: r216260