Implement P0614R1, Range-based for statements with initializer.

Implement P0614R1, Range-based for statements with initializer.

	* parser.c (cp_parser_range_based_for_with_init_p): New.
	(cp_parser_init_statement): Use it.  Parse the optional init-statement
	for a range-based for loop.
	(cp_parser_skip_to_closing_parenthesis_1): Handle balancing ?:.

	* g++.dg/cpp2a/range-for1.C: New test.
	* g++.dg/cpp2a/range-for2.C: New test.
	* g++.dg/cpp2a/range-for3.C: New test.
	* g++.dg/cpp2a/range-for4.C: New test.
	* g++.dg/cpp2a/range-for5.C: New test.
	* g++.dg/cpp2a/range-for6.C: New test.
	* g++.dg/cpp2a/range-for7.C: New test.

From-SVN: r260619