Add librt to default libs on linux

sandbox/linux/BUILD.gn

 # Copyright 2014 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("//build/config/nacl/config.gni")
 import("//testing/test.gni")
 
 if (is_android) {
   import("//build/config/android/rules.gni")
@@ skipping 101 matching lines @@
     ":sandbox_linux_test_utils",
     "//base",
     "//testing/gtest",
   ]
 
   if (use_base_test_suite) {
     deps += [ "//base/test:test_support" ]
     defines = [ "SANDBOX_USES_BASE_TEST_SUITE" ]
   }
 
-  if (is_linux) {
-    # Don't use this on Android.
-    libs = [ "rt" ]
-  }
-
   if (compile_suid_client) {
     sources += [
       "suid/client/setuid_sandbox_client_unittest.cc",
       "suid/client/setuid_sandbox_host_unittest.cc",
     ]
   }
   if (use_seccomp_bpf) {
     sources += [
       "bpf_dsl/bpf_dsl_unittest.cc",
       "bpf_dsl/codegen_unittest.cc",
@@ skipping 323 matching lines @@
     }
   }
 
   test_runner_script("sandbox_linux_unittests__test_runner_script") {
     test_name = "sandbox_linux_unittests"
     test_type = "gtest"
     test_suite = "sandbox_linux_unittests"
     isolate_file = "//sandbox/sandbox_linux_unittests_android.isolate"
   }
 }