Check __GLIBC_PREREQ availability before use.

webrtc/system_wrappers/source/cpu_features_linux.c

 /*
  *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #include <stdlib.h>
 #include <string.h>
 #include <features.h>
+#ifndef __GLIBC_PREREQ
+#define __GLIBC_PREREQ(a, b) 0
+#endif
 #if __GLIBC_PREREQ(2, 16)
 #include <sys/auxv.h>
 #else
 #include <fcntl.h>
 #include <unistd.h>
 #include <errno.h>
 #include <link.h>
 #endif
 #include "webrtc/system_wrappers/include/cpu_features_wrapper.h"
 
@@ skipping 50 matching lines @@
   if ((hwcap & HWCAP_NEON) != 0)
     result |= kCPUFeatureNEON;
 #endif
   if (architecture >= 7)
     result |= kCPUFeatureARMv7;
   if (architecture >= 6)
     result |= kCPUFeatureLDREXSTREX;
   return result;
 }
 #endif  // WEBRTC_ARCH_ARM_FAMILY