Add librt to default libs on linux

device/BUILD.gn

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/features.gni")
 import("//testing/test.gni")
 
 if (is_android) {
   import("//build/config/android/rules.gni")  # For generate_jni().
 }
@@ skipping 152 matching lines @@
       "bluetooth/bluetooth_advertisement_bluez_unittest.cc",
       "bluetooth/bluetooth_audio_sink_bluez_unittest.cc",
       "bluetooth/bluetooth_bluez_unittest.cc",
       "bluetooth/bluetooth_gatt_bluez_unittest.cc",
       "bluetooth/bluetooth_socket_bluez_unittest.cc",
     ]
 
     deps += [ "//dbus" ]
   }
 
-  if (is_posix && !is_android && !is_mac) {
-    libs = [ "rt" ]
-  }
-
   if (is_mac) {
     deps += [ "//third_party/ocmock" ]
     ldflags = [ "-ObjC" ]
     libs = [ "IOBluetooth.framework" ]
 
     # In the OSX 10.10 SDK, CoreBluetooth became a top level framework.
     # Previously, it was nested in IOBluetooth. In order for Chrome to run on
     # OSes older than OSX 10.10, the top level CoreBluetooth framework must be
     # weakly linked.
     if (mac_sdk_version == "10.10") {
@@ skipping 14 matching lines @@
   }
 
   android_library("bluetooth_test_java") {
     java_files = bluetooth_java_sources_needing_jni
     deps = [
       "//base:base_java",
       "//device/bluetooth:java",
     ]
   }
 }