Fix for 13086 -- build pre-reqs explicitly in other pnacl buildbot script.
Fix for 13086 -- build pre-reqs explicitly in other pnacl buildbot script.

r13086 removed the implicit pre-reqs library building from the torture
test scripts and made it the responsibility of the buildbot script.
Added that to buildbot_pnacl_toolchain_tests.sh but not
buildbot_pnacl.sh, so add to buildbot_pnacl.sh now.

BUG=none (red bot)
R=dschuff@chromium.org, dyen@chromium.org

Review URL: https://codereview.chromium.org/255783006

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@13088 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client