Enable find-missing-symbols-at-link-time for chromeos builds too.

third_party/libexif/libexif.gyp

 # Copyright (c) 2012 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 == "linux" and chromeos==0', {
         'use_system_libexif%': 1,
       }, {  # OS != "linux" and chromeos==0
@@ skipping 46 matching lines @@
               '-Wno-enum-conversion',
               '-Wno-switch',
               '-Wno-format',
               # libexif uses fabs(int) to cast to float.
               '-Wno-absolute-value',
             ],
           },
           'conditions': [
             ['os_posix==1 and OS!="mac"', {
               'cflags!': ['-fvisibility=hidden'],
+              'libraries': ['-lm'],
             }],
             ['OS=="mac"', {
               'conditions': [
                ['mac_breakpad==1', {
                   'variables': {
                     'mac_real_dsym': 1,
                   },
                }],
               ],
               'xcode_settings': {
@@ skipping 50 matching lines @@
             ],
             'defines': [
               'USE_SYSTEM_LIBEXIF',
             ],
           },
         }
       ],
     }],
   ]
 }