Merge branch 'ps/reftable-sans-compat-util'

Merge branch 'ps/reftable-sans-compat-util'

Make the code in reftable library less reliant on the service
routines it used to borrow from Git proper, to make it easier to
use by external users of the library.

* ps/reftable-sans-compat-util:
  Makefile: skip reftable library for Coccinelle
  reftable: decouple from Git codebase by pulling in "compat/posix.h"
  git-compat-util.h: split out POSIX-emulating bits
  compat/mingw: split out POSIX-related bits
  reftable/basics: introduce `REFTABLE_UNUSED` annotation
  reftable/basics: stop using `SWAP()` macro
  reftable/stack: stop using `sleep_millisec()`
  reftable/system: introduce `reftable_rand()`
  reftable/reader: stop using `ARRAY_SIZE()` macro
  reftable/basics: provide wrappers for big endian conversion
  reftable/basics: stop using `st_mult()` in array allocators
  reftable: stop using `BUG()` in trivial cases
  reftable/record: don't `BUG()` in `reftable_record_cmp()`
  reftable/record: stop using `BUG()` in `reftable_record_init()`
  reftable/record: stop using `COPY_ARRAY()`
  reftable/blocksource: stop using `xmmap()`
  reftable/stack: stop using `write_in_full()`
  reftable/stack: stop using `read_in_full()`