level 1: variable 0, env 1
level 2: variable 1, env 2
level 3: variable 2, env 3
: set-env-same
ok
: set-env-different
make: Cannot override read-only global variable ".MAKE.LEVEL.ENV" with a command line variable
	in make[1] in directory "<curdir>"
make: Fatal errors encountered -- cannot continue
make: stopped making "ok" in unit-tests
set-env-different: exit 1
exit status 0