Currently Cargo doesn't set the `MAKEFLAGS` variable,
but it's free for build scripts invoking GNU Make
to set it to the contents of `CARGO_MAKEFLAGS`.
+* `CARGO_PRIMARY_PACKAGE` — This environment variable will be set if the package being
+ built is primary. Primary packages are the ones the user
+ selected on the command-line, either with `-p` flags or
+ the defaults based on the current directory and the default
+ workspace members.
+ This environment variable will not be set when building dependencies.
* `CARGO_FEATURE_<name>` — For each activated feature of the package being
built, this environment variable will be present
where `<name>` is the name of the feature uppercased