so that this is safe even if VARIABLE is longer than kern.argmax.
There is another instance of CFILES which might need the same treatment,
and might be noticed when doing a "make links".
The same has to be done in RELENG_4 (on some different file).
Noticed-by: picobsd cross-compiling LINT
Suggested-by: Alfred (bright@mu.org), des@freebsd.org
MFC-after: 3 days