re PR middle-end/13696 (enum not useable as array index?)

re PR middle-end/13696 (enum not useable as array index?)

	PR middle-end/13696
	* fold-const.c (fold_convert): New function to provide type
	conversion to the middle-end without using convert.
	(negate_expr, associate_trees, size_diffop, omit_one_operand,
	operand_equal_for_comparison_p, pedantic_omit_one_operand,
	invert_truthvalue, optimize_bit_field_compare, range_binop,
	decode_field_reference, make_range, build_range_check, unextend,
	fold_truthop, extract_muldiv_1, fold_mathfn_compare,
	fold_binary_op_with_conditional_arg, fold_inf_compare,
	fold_single_bit_test, fold, multiple_of_p): Replace all calls to
	convert with calls to fold_convert.

	* g++.dg/opt/fold1.C: New test case.

From-SVN: r77464