Fix clang warnings in GN build.

third_party/opus/opus.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': [
       ['target_arch=="arm" or target_arch=="armv7" or target_arch=="arm64"', {
         'use_opus_fixed_point%': 1,
       }, {
@@ skipping 41 matching lines @@
         }, {
           'defines': [
             'USE_ALLOCA',
             'inline=__inline',
           ],
           'msvs_disabled_warnings': [
             4305,  # Disable truncation warning in celt/pitch.c .
             4334,  # Disable 32-bit shift warning in src/opus_encoder.c .
           ],
         }],
+        ['os_posix==1', {
+          'link_settings': {
+            'libraries': [ '-lm' ],
+          },
+        }],
         ['os_posix==1 and OS!="android"', {
           # Suppress a warning given by opus_decoder.c that tells us
           # optimizations are turned off.
           'cflags': [
             '-Wno-#pragma-messages',
           ],
           'xcode_settings': {
             'WARNING_CFLAGS': [
               '-Wno-#pragma-messages',
             ],
@@ skipping 55 matching lines @@
           'defines': [
             'inline=__inline',
           ],
         }],
         ['OS=="android"', {
           'link_settings': {
             'libraries': [
               '-llog',
             ],
           },
+        }],
+        ['clang==1', {
+          'cflags': [ '-Wno-absolute-value' ],
         }]
       ],
       'sources': [
         'src/src/opus_demo.c',
       ],
       'include_dirs': [
         'src/celt',
         'src/silk',
       ],
     },  # target opus_demo
   ]
 }