Ignore mesh_pipeline Xcode build files.
Ignore mesh_pipeline Xcode build files.

Tested: mesh_pipeline with cmake -GXcode doesn't generate any
non-ignored files.

Change-Id: Ibbbd2e3afe105a612970802a3cf6678e34876d51

google/fplbase,google/fplbase,google/fplbase,google/fplbase