message: util: Conditionalize some syscalls in syscall name table
  Put these in `#ifdef` as they are newer syscalls that might not be
  defined on all kernels:
  __NR_pkey_alloc
  __NR_pkey_free
  __NR_pkey_mprotect
  __NR_preadv2
  __NR_pwritev2
  Thanks to jamesob for reporting.
diff: @@ -272,15 +272,23 @@ const std::map<uint32_t, std::string> LINUX_SYSCALLS{
  {__NR_pipe, "pipe"},
  {__NR_pipe2, "pipe2"},
  {__NR_pivot_root, "pivot_root"},
  +#ifdef __NR_pkey_alloc
  {__NR_pkey_alloc, "pkey_alloc"},
  +#endif
  +#ifdef __NR_pkey_free
  {__NR_pkey_free, "pkey_free"},
  +#endif
  +#ifdef __NR_pkey_mprotect
  {__NR_pkey_mprotect, "pkey_mprotect"},
  +#endif
  {__NR_poll, "poll"},
  {__NR_ppoll, "ppoll"},
  {__NR_prctl, "prctl"},
  {__NR_pread64, "pread64"},
  {__NR_preadv, "preadv"},
  +#ifdef __NR_preadv2
  {__NR_preadv2, "preadv2"},
  +#endif
  {__NR_prlimit64, "prlimit64"},
  {__NR_process_vm_readv, "process_vm_readv"},
  {__NR_process_vm_writev, "process_vm_writev"},
  @@ -289,7 +297,9 @@ const std::map<uint32_t, std::string> LINUX_SYSCALLS{
  {__NR_putpmsg, "putpmsg"},
  {__NR_pwrite64, "pwrite64"},
  {__NR_pwritev, "pwritev"},
  +#ifdef __NR_pwritev2
  {__NR_pwritev2, "pwritev2"},
  +#endif
  {__NR_query_module, "query_module"},
  {__NR_quotactl, "quotactl"},
  {__NR_read, "read"},
  