Bug 1732208 - Silence the unused-but-set-variable warning in ipc. r=mccr8

ipc/chromium/src/chrome/common/ipc_channel_win.cc(133,8): error: variable 'waited' set but not used [-Werror,-Wunused-but-set-variable]
  bool waited = false;
       ^
ipc/mscom/InterceptorLog.cpp(183,12): error: variable 'rv' set but not used [-Werror,-Wunused-but-set-variable]
  nsresult rv = mThread->Dispatch(
           ^

Differential Revision: https://phabricator.services.mozilla.com/D126455

ipc/chromium/src/chrome/common/ipc_channel_win.cc

@@ -130,10 +130,8 @@ HANDLE Channel::ChannelImpl::GetServerPipeHandle() const { return pipe_; }
 void Channel::ChannelImpl::Close() {
   ASSERT_OWNINGTHREAD(ChannelImpl);
 
-  bool waited = false;
   if (input_state_.is_pending || output_state_.is_pending) {
     CancelIo(pipe_);
-    waited = true;
   }
 
   // Closing the handle at this point prevents us from issuing more requests

ipc/mscom/InterceptorLog.cpp

@@ -187,6 +187,7 @@ nsresult Logger::Shutdown() {
 
   rv = mThread->Shutdown();
   NS_WARNING_ASSERTION(NS_SUCCEEDED(rv), "Shutdown failed");
+  (void)rv;
   return NS_OK;
 }