wl: silence unused code warnings

When wl-dmabuf is not enabled, rustc complains about unused imports and
enum values.  Add compiler directives to silence the warnings.

BUG=None
TEST='cargo build', 'emerge-nami crosvm'

Change-Id: Ib39735d329f8aa835c0b5842b10bfe78d0e578d9
Signed-off-by: Daniel Verkamp <dverkamp@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1327827

devices/src/virtio/wl.rs

@@ -57,6 +57,7 @@ use data_model::VolatileMemoryError;
 use data_model::*;
 
 use msg_socket::{MsgError, MsgReceiver, MsgSender, MsgSocket};
+#[cfg(feature = "wl-dmabuf")]
 use resources::GpuMemoryDesc;
 use sys_util::{
     pipe, round_up_to_page_size, Error, EventFd, FileFlags, GuestAddress, GuestMemory,
@@ -403,6 +404,7 @@ fn encode_resp(desc_mem: VolatileSlice, resp: WlResp) -> WlResult<u32> {
     }
 }
 
+#[allow(dead_code)]
 #[derive(Debug)]
 enum WlError {
     NewAlloc(Error),

resources/src/gpu_allocator.rs

@@ -12,6 +12,7 @@ use gpu_buffer;
 use msg_socket::MsgOnSocket;
 use sys_util;
 
+#[allow(dead_code)]
 #[derive(Debug)]
 pub enum GpuAllocatorError {
     OpenGpuBufferDevice,