Fix fplviewer build.
Fix fplviewer build.

Recent changes somehow removed fplbase's generated include dir
from the fplviewer build. This is actually correct. It should
be included explicitly.

Add explicit include of fplbase's generated include dir.

Change-Id: I84057f383c1d8a51f45356a823e311763eea8490
Tested: fplviewer now builds on Linux.

google/motive,google/motive