Use MacOS helper to get address of environ variable

runtime/bin/process_macos.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/globals.h"
 #if defined(TARGET_OS_MACOS)
 
 #include "bin/process.h"
 
+#include <crt_externs.h>  // NOLINT
 #include <errno.h>  // NOLINT
 #include <fcntl.h>  // NOLINT
 #include <poll.h>  // NOLINT
 #include <signal.h>  // NOLINT
 #include <stdio.h>  // NOLINT
 #include <stdlib.h>  // NOLINT
 #include <string.h>  // NOLINT
 #include <unistd.h>  // NOLINT
 
 #include "bin/fdutils.h"
 #include "bin/lockers.h"
 #include "bin/log.h"
 #include "bin/thread.h"
 
 #include "platform/signal_blocker.h"
 
 
-extern char **environ;
-
 
 namespace dart {
 namespace bin {
 
 // ProcessInfo is used to map a process id to the file descriptor for
 // the pipe used to communicate the exit code of the process to Dart.
 // ProcessInfo objects are kept in the static singly-linked
 // ProcessInfoList.
 class ProcessInfo {
  public:
@@ skipping 428 matching lines @@
         ReportChildError(exec_control[1]);
       }
       VOID_TEMP_FAILURE_RETRY(close(read_err[1]));
 
       if (working_directory != NULL &&
           TEMP_FAILURE_RETRY(chdir(working_directory)) == -1) {
         ReportChildError(exec_control[1]);
       }
 
       if (program_environment != NULL) {
+        // On MacOS you have to do a bit of magic to get to the
+        // environment strings.
+        char** environ = *(_NSGetEnviron());
         environ = program_environment;
       }
 
       VOID_TEMP_FAILURE_RETRY(
           execvp(path, const_cast<char* const*>(program_arguments)));
 
       ReportChildError(exec_control[1]);
     }
   }
 
@@ skipping 398 matching lines @@
     bzero(&act, sizeof(act));
     act.sa_handler = SIG_DFL;
     VOID_NO_RETRY_EXPECTED(sigaction(signal, &act, NULL));
   }
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_MACOS)