cannot print u0 or use u0 in var args

[kristate]

const std = @import("std");
test "print u0" {
  var uz: u0 = 0;
  std.debug.warn("uz: {}", uz);
}

/Users/cfkk/Source/zig2/build/lib/zig/std/debug/index.zig:46:23: error: compiler bug: var args can't handle void. https://github.com/ziglang/zig/issues/557
    stderr.print(fmt, args) catch return;
                      ^
/Users/cfkk/Source/zig2/build/u0.zig:4:17: note: called from here
  std.debug.warn("uz: {}", uz);
                ^

related: #557 #1530

[andrewrk]

duplicate of #557