newvers.sh: Don't use return to exit.

[jhb]

Summary

Commit acfb506b3d00 replaced an exit 0 when using -V with a return
instead. FreeBSD's sh treats a return outside of a function like
exit, but this is a non-portable extension. Other Bourne shells only
permit return to be used within a function and continue execution
(possibly with a warning).

To fix, don't reuse VARS_ONLY (which is intended to be set by other
scripts before sourcing newvers.sh directly) and instead use a new
variable (VARS_ONLY_EXIT) to restore the use of exit for the
non-sourced case.

Obtained from: CheriBSD
Sponsored by: DARPA

[emaste]

sys/conf/newvers.sh

138

could we just make this exit 0?

[jhb]

sys/conf/newvers.sh

138

No. The intended use case is something like:

#/bin/sh

...
VARS_ONLY=1
. /path/to/sys/conf/newvers.sh
...

If you called exit 0 here you would exit that outer script rather than returning to the next line in the outer script.

[imp]

This looks good to me.