Separate out build steps on toolchain build bot - so we can better diagnose  where the flakiness comes from.
Separate out build steps on toolchain build bot - so we can better diagnose  where the flakiness comes from.

Also: 
* added more comments 
* eliminated the situation where
two conflicting flags -jX and -j1 were passed to scons
* eliminated duplicate bitcode=1 flags

BUG= flaky bot:  linux-pnacl-x86_64-tests-arm
Review URL: https://codereview.chromium.org/11269046

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@10100 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

nacl-webkit/native_client,nacl-webkit/native_client,sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,nacl-webkit/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client