support/download/cvs: use appropriate TAR

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Signed-off-by: Arnout Vandecappelle <arnout@mind.be>
(cherry picked from commit c013836ae6c3026aae16a0465ddc1288274e63ee)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

support/download/cvs

@@ -68,4 +68,4 @@ export TZ=UTC
 _cvs ${quiet} -z3 -d"'${uri}'" \
      co "${@}" -d "'${basename}'" ${select} "'${rev}'" -P "'${rawname}'"
 
-tar czf "${output}" "${basename}"
+${TAR} czf "${output}" "${basename}"