I am having trouble with sstate caching of my os-release.bbappend and
am stuck. The simple example file looks like something below, where I
am setting a variable from a computed python function. What's the magic
to make the find_version(d) always run but do_compile to only run if
VERSION changes? I basically want something like
`find_version[nostamp]="1"` but that seems to only work for tasks.

def find_version(d):
import subprocess
cmd = "git describe --long"
return subprocess.check_output(cmd).rstrip().decode('utf-8')

VERSION = "${@find_version(d)}"
# do_compile uses $VERSION