Take the location of gflags from a variable passed in by the parent script.

The build of glog as part of the Cobalt stand-alone CMake build was failing
on my new laptop (even though it seems to work on the build bot and on other
people's dev machines.) I believe this
is because the build was linking against the version of gflags that happened
to be on the build machine and my new laptop must have an older version
of gflags.

Change-Id: I3c54f73042dfd19cad953bd01341a38e4eb4a779
1 file changed