Build ESR 91 against newer Linux kernel headers

[llewelld]

ESR 91 introduced some membarrier code that needs newer Linux kernel headers.

The following commit patches around this to avoid the need for the headers 5a88215c32d63ba40125afa722a6ee8680a49968.

However, this change may not be correct. In particular the _NR_membarrier value (which I set to 283) is platform-independent. It may not be correct, certainly unlikely to be for both arm and i486. So this needs to be fixed.

One fix would be to build against Linux kernel headers 4.16 or newer.

See:

1. https://phabricator.services.mozilla.com/D88395
2. https://github.com/sailfishos/kernel-headers
3. https://man7.org/linux/man-pages/man2/membarrier.2.html