linux/gyp: Find missing symbols at build time, not runtime.

media/media_cdm.gypi

 # Copyright 2013 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.
 
 {
   'variables': {
     'conditions': [
       ['OS == "android"', {
         # Android doesn't use ffmpeg.
         'use_ffmpeg%': 0,
@@ skipping 127 matching lines @@
             'clearkeycdmadapter_resources',
           ],
           'sources': [
             '<(SHARED_INTERMEDIATE_DIR)/clearkeycdmadapter_version.rc',
           ],
           'conditions': [
             ['os_posix == 1 and OS != "mac" and enable_pepper_cdms==1', {
               # Because clearkeycdm has type 'loadable_module' (see comments),
               # we must explicitly specify this dependency.
               'libraries': [
+               '-lrt',
                 # Built by clearkeycdm.
                 '<(PRODUCT_DIR)/libclearkeycdm.so',
               ],
             }],
           ],
         },
       ],
     }],
   ],
 }