Conditionally compile gflag dependencies. Add data_fitting.cc to the cmake file.
Conditionally compile gflag dependencies.
Add data_fitting.cc to the cmake file.

Based on a patch by Casey Goodlett.

Change-Id: Iab17ae91e6fe26b3e01d430154e2f5cdbc1abca5

DougFirErickson/ceres-solver,arnaudgelas/ceres-solver,entylop/ceres-solver,caomw/ceres-solver,stonier/ceres_solver,jmwalls/ceres-solver-fork,stonier/ceres_solver,entylop/ceres-solver,vedanshu95/ceres-solver,timfel/ceres-bin,whuaegeanse/ceres-solver,kartikkumar/ceres-solver,ysonggit/ceres-solver,vedanshu95/ceres-solver,DougFirErickson/ceres-solver,ikoruk/ceres-solver,ysonggit/ceres-solver,pritasam/ceres-solver,ysonggit/ceres-solver,jmwalls/ceres-solver-fork,stonier/ceres_solver,ikoruk/ceres-solver,ikoruk/ceres-solver,jmwalls/ceres-solver-fork,ikoruk/ceres-solver,timfel/ceres-bin,techoe/ceres-solver,timfel/ceres-bin,pritasam/ceres-solver,ikoruk/ceres-solver,whuaegeanse/ceres-solver,stonier/ceres_solver,whuaegeanse/ceres-solver,entylop/ceres-solver,timfel/ceres-bin,caomw/ceres-solver,ysonggit/ceres-solver,vedanshu95/ceres-solver,kartikkumar/ceres-solver,techoe/ceres-solver,whuaegeanse/ceres-solver,arnaudgelas/ceres-solver,entylop/ceres-solver,caomw/ceres-solver,techoe/ceres-solver,pritasam/ceres-solver,DougFirErickson/ceres-solver,kartikkumar/ceres-solver,jmwalls/ceres-solver-fork,kartikkumar/ceres-solver,arnaudgelas/ceres-solver,DougFirErickson/ceres-solver