Correct the sign of exit codes for the process library.

runtime/bin/process_macos.cc

 // Copyright (c) 2011, 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 "bin/process.h"
 
 #include <errno.h>
 #include <fcntl.h>
 #include <signal.h>
 #include <stdio.h>
@@ skipping 71 matching lines @@
                                    int os_error_message_len) {
   SafeStrNCpy(os_error_message, strerror(errno), os_error_message_len);
 }
 
 
 void ExitHandler(int process_signal, siginfo_t* siginfo, void* tmp) {
   int pid = 0;
   int status = 0;
   while ((pid = waitpid(-1, &status, WNOHANG)) > 0) {
     int exit_code = 0;
-    // TODO(ager): Transform exit_code 255 to -1.
-    if (WIFEXITED(status)) exit_code = WEXITSTATUS(status);
-    // TODO(ager): Transform termsig to -termsig to destinguish from
-    // exit codes.
-    if (WIFSIGNALED(status)) exit_code = WTERMSIG(status);
+    int negative = 0;
+    if (WIFEXITED(status)) {
+      exit_code = WEXITSTATUS(status);
+      if (exit_code == 255) {
+        exit_code = 1;
+        negative = 1;
+      }
+    }
+    if (WIFSIGNALED(status)) {
+      exit_code = WTERMSIG(status);
+      negative = 1;
+    }
     ProcessInfo* process = LookupProcess(pid);
     if (process != NULL) {
-      intptr_t message[2] = { pid, exit_code };
+      int message[3] = { pid, exit_code, negative };
       intptr_t result =
           FDUtils::WriteToBlocking(process->fd(), &message, sizeof(message));
       if (result != sizeof(message)) {
         perror("ExitHandler notification failed");
       }
       close(process->fd());
     }
   }
 }
 
@@ skipping 217 matching lines @@
   if (result == -1) {
     return false;
   }
   return true;
 }
 
 
 void Process::Exit(intptr_t id) {
   RemoveProcess(id);
 }