gn/linux: warnings as errors, turn on Wextra

build/secondary/third_party/libsrtp/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.
 
 declare_args() {
   use_system_libsrtp = false
 }
 
 config("libsrtp_config") {
   defines = [
@@ skipping 194 matching lines @@
         "srtp/include/rtp.h",
         "srtp/include/srtp.h",
         "srtp/crypto/include/datatypes.h",
         "srtp/test/getopt_s.c",
         "srtp/test/rtp.c",
         "srtp/test/rtpw.c",
       ]
       if (is_android) {
         defines = [ "HAVE_SYS_SOCKET_H" ]
       }
+      if (is_clang) {
+        cflags = [ "-Wno-implicit-function-declaration" ]
+      }
     }
 
     executable("srtp_test_cipher_driver") {
       configs -= [ "//build/config/compiler:chromium_code" ]
       configs += [ "//build/config/compiler:no_chromium_code" ]
       deps = [ ":libsrtp" ]
       sources = [
         "srtp/crypto/test/cipher_driver.c",
       ]
     }
@@ skipping 73 matching lines @@
         ":srtp_test_stat_driver",
         ":srtp_test_sha1_driver",
         ":srtp_test_kernel_driver",
         ":srtp_test_aes_calc",
         ":srtp_test_rand_gen",
         ":srtp_test_env",
       ]
     }
   }
 }