make runtest fails

[me]

I am trying to install caffe for Titan X GPU without Anaconda.

I passed make -j8 all and make -j8 test but make -j8 runtest gives me the following error :

```
.build_release/tools/caffe: symbol lookup error: .build_release/tools/caffe: undefined symbol: _ZN5caffe3NetIfE21CopyTrainedLayersFromERKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE
Makefile:543: recipe for target 'runtest' failed
make: *** [runtest] Error 127

```

### System configuration
* Operating system: Ubuntu 18.04
* Compiler: gcc 7.3
* CUDA version (if applicable): 9.1
* CUDNN version (if applicable): 7.1
* BLAS: atlas
* Python version (if using pycaffe): 3.6

Any clues