Save and restore errno in signal handler.

runtime/bin/process_macos.cc

Index: runtime/bin/process_macos.cc
diff --git a/runtime/bin/process_macos.cc b/runtime/bin/process_macos.cc
index c42b08114d0991e99a2df5d0976f3077b550afe7..1d0c5e9d17d6bbb0829fb1a4bf8f3469968a2b5d 100644
--- a/runtime/bin/process_macos.cc
+++ b/runtime/bin/process_macos.cc
@@ -87,6 +87,8 @@ static void SetChildOsErrorMessage(char* os_error_message,
 void ExitHandler(int process_signal, siginfo_t* siginfo, void* tmp) {
   int pid = 0;
   int status = 0;
+  // Save errno so it can be restored at the end.
+  int entry_errno = errno;
   while ((pid = TEMP_FAILURE_RETRY(waitpid(-1, &status, WNOHANG))) > 0) {
     int exit_code = 0;
     int negative = 0;
@@ -108,6 +110,7 @@ void ExitHandler(int process_signal, siginfo_t* siginfo, void* tmp) {
       TEMP_FAILURE_RETRY(close(process->fd()));
     }
   }
+  errno = entry_errno;
 }