Fixup CMake file to allow inclusion via add_subdirectory() in Cobalt.

We are incorporating lossmin into the Cobalt build via
an add_subdirectory() clause in the top-level CMake file.
We found we needed to make these changes for that to succeed.

Change-Id: Ie7f337538b6db00ee299a197e7c132458c15a843
1 file changed