build failure with ocaml installed

source issue: https://github.com/intel/compute-runtime/issues/39

I was able to reproduce this using Ubuntu 18.04 (LTS). steps:
1. prepare workspace with opencl-clang ingredients
2. use clean Ubuntu 18.04 and execute folowing commands:
```
apt-get update
apt-get -y install cmake gcc g++ clang-4.0 bison flex git patch ocaml-findlib libctypes-ocaml-dev

cmake ../common_clang/ -DCMAKE_BUILD_TYPE=Release
make -j8 cclang
```

at the end I get:
> CMake Error at docs/cmake_install.cmake:41 (file):
file INSTALL cannot find
"/workspace/build/src/docs/ocamldoc/html/.".
Call Stack (most recent call first):
cmake_install.cmake:73 (include)

optionally you can use existing Ubuntu 18.04 and install packages listed above.