Fix for gflags with pthreads linking. Patch from Alex Stewart of Ceres
Fix for gflags with pthreads linking. Patch from Alex Stewart of Ceres

Change-Id: Iad78fa17d40be4483acdce22502bdc16e29d0e99

klemmster/TheiaSfM,zhanshenman/TheiaSfM,klemmster/TheiaSfM,zhanshenman/TheiaSfM,rajvishah/TheiaSfM,klemmster/TheiaSfM,rajvishah/TheiaSfM,zhanshenman/TheiaSfM,mylxiaoyi/TheiaSfM,whuaegeanse/TheiaSfM,klemmster/TheiaSfM,rajvishah/TheiaSfM,whuaegeanse/TheiaSfM,mylxiaoyi/TheiaSfM,mylxiaoyi/TheiaSfM,mylxiaoyi/TheiaSfM,klemmster/TheiaSfM,whuaegeanse/TheiaSfM,mylxiaoyi/TheiaSfM,zhanshenman/TheiaSfM,zhanshenman/TheiaSfM,whuaegeanse/TheiaSfM,rajvishah/TheiaSfM