Missing bits from N4268, constant evaluation for all non-type args.

Missing bits from N4268, constant evaluation for all non-type args.

	* call.c (build_converted_constant_expr): Rename from
	build_integral_nontype_arg_conv, handle all types.
	* pt.c (convert_nontype_argument): In C++17 call it for all types.
	Move NOP stripping inside pointer case, don't strip ADDR_EXPR.
	* cvt.c (strip_fnptr_conv): Also strip conversions to the same type.

From-SVN: r249089