message: Don't error out if meta directory already exists
  Summary:
  The redex-generated scripts to rerun a crashing Redex run under gdb were
  erroring out because of this.
diff: @@ -387,7 +387,7 @@ Arguments parse_args(int argc, char* argv[]) {
  std::string metafiles = args.out_dir + "/meta/";
  int status = mkdir(metafiles.c_str(), 0755);
  - if (status != 0) {
  + if (status != 0 && errno != EEXIST) {
  // Attention: errno may get changed by syscalls or lib functions.
  // Saving before printing is a conventional way of using errno.
  int errsv = errno;
  