re PR c/39495 (OMP parallel loop w/ unsigned index var rejected)

	PR c/39495
	* c-parser.c (c_parser_omp_for_loop): Call c_parser_binary_expression
	instead of c_parser_expression_conv, if original_code isn't one of the
	4 allowed comparison codes, fail.

	* semantics.c (handle_omp_for_class_iterator): Swap cond operands and
	code if iter is the second operand.
	* parser.c (cp_parser_binary_expression): Add no_toplevel_fold_p
	argument.  If it is set, don't build the toplevel expression with
	build_x_binary_op, but build2.
	(cp_parser_assignment_expression,  cp_parser_omp_for_incr): Adjust
	callers.
	(cp_parser_omp_for_cond): Don't assume the first operand of the
	comparison must be decl.

	* gcc.dg/gomp/pr39495-2.c: Remove xfails.

	* testsuite/libgomp.c/loop-12.c: New test.
	* testsuite/libgomp.c/loop-11.c: New test.
	* testsuite/libgomp.c++/loop-11.C: New test.
	* testsuite/libgomp.c++/loop-12.C: New test.
	* testsuite/libgomp.c++/for-8.C: New test.

From-SVN: r145014