Build fail with glog-0.7.0 about gnss-sdr

[wkazubski]

The build can be fixed by adding the following line to toplevel CmakeFile.txt:

add_definitions(-DGLOG_USE_GLOG_EXPORT)

if glog is compiled as a external library or

add_definitions(-DGLOG_USE_GLOG_NO_EXPORT)

if it should be linked statically.
openSUSE has glog as a system library, so the first version should be used.
I am not sure where is the best place for this line (or lines) to work for both system and locally built glog.

[wkazubski]

Next is building OK now.