tree fd6bc3b590370bbc87d7b7536b15ee599d94c183
parent cd33a7c8f162e530ba1bcac2d450ca8eef9f7b78
author Ying Wang <wangying@google.com> 1360785002 -0800
committer Ying Wang <wangying@google.com> 1360785465 -0800

Dont' write out the clean_steps.mk if

If this is mm/mmm and there is no pre-existing clean_steps.mk.
Otherwise, the build system will run almost all the clean steps in the
sourcet tree if you do a full build next.

Change-Id: I5fe1e99c4f09629e4455319ea664cfba4ac634ea