Replaced strerror() calls with threadsafe strerror_r()

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 33351814675c46b4420a8d29cb4925f166f07f43..c87523c39194ab4e7b47d3dd611fc86934769d19 100644
--- a/runtime/bin/process_macos.cc
+++ b/runtime/bin/process_macos.cc
@@ -268,7 +268,10 @@ dart::Monitor* ExitCodeHandler::thread_terminate_monitor_ = new dart::Monitor();
 
 
 static void SetChildOsErrorMessage(char** os_error_message) {
-  *os_error_message = strdup(strerror(errno));
+  const int kBufferSize = 1024;
+  char error_message[kBufferSize];
+  strerror_r(errno, error_message, kBufferSize);
+  *os_error_message = strdup(error_message);
 }
 
 
@@ -291,7 +294,9 @@ static void ReportChildError(int exec_control_fd) {
   // In the case of failure in the child process write the errno and
   // the OS error message to the exec control pipe and exit.
   int child_errno = errno;
-  char* os_error_message = strerror(errno);
+  const int kBufferSize = 1024;
+  char os_error_message[kBufferSize];
+  strerror_r(errno, os_error_message, kBufferSize);
   ASSERT(sizeof(child_errno) == sizeof(errno));
   int bytes_written =
       FDUtils::WriteToBlocking(