Merge branch 'ps/reftable-sans-compat-util' into ps/reftable-api-revamp

Merge branch 'ps/reftable-sans-compat-util' into ps/reftable-api-revamp

* 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()`