Jeff King [off-list ref] writes:

quoted

    I ended up avoiding write_or_die() primarily because there is
    nothing "Git" about this helper, which is a poor-man's emulation
    of "dd if=/dev/zero".  It felt a bit too much to pull cache.h in
    as dependency for it.

I don't find it any more "Git" than xwrite() or die_errno(), really, but
I am quite happy with what you have here.

True.  I view "git-compat-util.h" as "projects, not limited to Git,
would benefit by its help to use POSIX api more sensibly", while
"cache.h" is "things that are about Git".  write_or_die() is certainly
in the former category, but is not available without "cache.h" X-<.